*
* Copyright (C) 2002, Linus Torvalds
*
- * 09Apr2002 akpm@zip.com.au
+ * 09Apr2002 Andrew Morton
* Initial version.
*/
#include <linux/kernel.h>
#include <linux/fs.h>
+#include <linux/gfp.h>
#include <linux/mm.h>
-#include <linux/module.h>
+#include <linux/export.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
+#include <linux/task_io_accounting_ops.h>
#include <linux/pagevec.h>
-
-struct backing_dev_info default_backing_dev_info = {
- .ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE,
- .state = 0,
-};
-
-EXPORT_SYMBOL_GPL(default_backing_dev_info);
+#include <linux/pagemap.h>
/*
- * Initialise a struct file's readahead state
+ * Initialise a struct file's readahead state. Assumes that the caller has
+ * memset *ra to zero.
*/
void
file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
{
- memset(ra, 0, sizeof(*ra));
ra->ra_pages = mapping->backing_dev_info->ra_pages;
+ ra->prev_pos = -1;
}
+EXPORT_SYMBOL_GPL(file_ra_state_init);
-EXPORT_SYMBOL(file_ra_state_init);
+#define list_to_page(head) (list_entry((head)->prev, struct page, lru))
/*
- * Return max readahead size for this inode in number-of-pages.
+ * see if a page needs releasing upon read_cache_pages() failure
+ * - the caller of read_cache_pages() may have set PG_private or PG_fscache
+ * before calling, such as the NFS fs marking pages that are cached locally
+ * on disk, thus we need to give the fs a chance to clean up in the event of
+ * an error
*/
-static inline unsigned long get_max_readahead(struct file_ra_state *ra)
+static void read_cache_pages_invalidate_page(struct address_space *mapping,
+ struct page *page)
{
- return ra->ra_pages;
+ if (page_has_private(page)) {
+ if (!trylock_page(page))
+ BUG();
+ page->mapping = mapping;
+ do_invalidatepage(page, 0);
+ page->mapping = NULL;
+ unlock_page(page);
+ }
+ page_cache_release(page);
}
-static inline unsigned long get_min_readahead(struct file_ra_state *ra)
+/*
+ * release a list of pages, invalidating them first if need be
+ */
+static void read_cache_pages_invalidate_pages(struct address_space *mapping,
+ struct list_head *pages)
{
- return (VM_MIN_READAHEAD * 1024) / PAGE_CACHE_SIZE;
-}
+ struct page *victim;
-#define list_to_page(head) (list_entry((head)->prev, struct page, list))
+ while (!list_empty(pages)) {
+ victim = list_to_page(pages);
+ list_del(&victim->lru);
+ read_cache_pages_invalidate_page(mapping, victim);
+ }
+}
/**
- * read_cache_pages - populate an address space with some pages, and
- * start reads against them.
+ * read_cache_pages - populate an address space with some pages & start reads against them
* @mapping: the address_space
* @pages: The address of a list_head which contains the target pages. These
* pages have their ->index populated and are otherwise uninitialised.
* Hides the details of the LRU cache etc from the filesystems.
*/
int read_cache_pages(struct address_space *mapping, struct list_head *pages,
- int (*filler)(void *, struct page *), void *data)
+ int (*filler)(void *, struct page *), void *data)
{
struct page *page;
- struct pagevec lru_pvec;
int ret = 0;
- pagevec_init(&lru_pvec, 0);
-
while (!list_empty(pages)) {
page = list_to_page(pages);
- list_del(&page->list);
- if (add_to_page_cache(page, mapping, page->index, GFP_KERNEL)) {
- page_cache_release(page);
+ list_del(&page->lru);
+ if (add_to_page_cache_lru(page, mapping,
+ page->index, GFP_KERNEL)) {
+ read_cache_pages_invalidate_page(mapping, page);
continue;
}
+ page_cache_release(page);
+
ret = filler(data, page);
- if (!pagevec_add(&lru_pvec, page))
- __pagevec_lru_add(&lru_pvec);
- if (ret) {
- while (!list_empty(pages)) {
- struct page *victim;
-
- victim = list_to_page(pages);
- list_del(&victim->list);
- page_cache_release(victim);
- }
+ if (unlikely(ret)) {
+ read_cache_pages_invalidate_pages(mapping, pages);
break;
}
+ task_io_account_read(PAGE_CACHE_SIZE);
}
- pagevec_lru_add(&lru_pvec);
return ret;
}
static int read_pages(struct address_space *mapping, struct file *filp,
struct list_head *pages, unsigned nr_pages)
{
+ struct blk_plug plug;
unsigned page_idx;
- struct pagevec lru_pvec;
- int ret = 0;
+ int ret;
+
+ blk_start_plug(&plug);
if (mapping->a_ops->readpages) {
ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
+ /* Clean up the remaining pages */
+ put_pages_list(pages);
goto out;
}
- pagevec_init(&lru_pvec, 0);
for (page_idx = 0; page_idx < nr_pages; page_idx++) {
struct page *page = list_to_page(pages);
- list_del(&page->list);
- if (!add_to_page_cache(page, mapping,
+ list_del(&page->lru);
+ if (!add_to_page_cache_lru(page, mapping,
page->index, GFP_KERNEL)) {
mapping->a_ops->readpage(filp, page);
- if (!pagevec_add(&lru_pvec, page))
- __pagevec_lru_add(&lru_pvec);
- } else {
- page_cache_release(page);
}
+ page_cache_release(page);
}
- pagevec_lru_add(&lru_pvec);
+ ret = 0;
+
out:
+ blk_finish_plug(&plug);
+
return ret;
}
/*
- * Readahead design.
- *
- * The fields in struct file_ra_state represent the most-recently-executed
- * readahead attempt:
- *
- * start: Page index at which we started the readahead
- * size: Number of pages in that read
- * Together, these form the "current window".
- * Together, start and size represent the `readahead window'.
- * next_size: The number of pages to read on the next readahead miss.
- * Has the magical value -1UL if readahead has been disabled.
- * prev_page: The page which the readahead algorithm most-recently inspected.
- * prev_page is mainly an optimisation: if page_cache_readahead
- * sees that it is again being called for a page which it just
- * looked at, it can return immediately without making any state
- * changes.
- * ahead_start,
- * ahead_size: Together, these form the "ahead window".
- * ra_pages: The externally controlled max readahead for this fd.
- *
- * When readahead is in the "maximally shrunk" state (next_size == -1UL),
- * readahead is disabled. In this state, prev_page and size are used, inside
- * handle_ra_miss(), to detect the resumption of sequential I/O. Once there
- * has been a decent run of sequential I/O (defined by get_min_readahead),
- * readahead is reenabled.
- *
- * The readahead code manages two windows - the "current" and the "ahead"
- * windows. The intent is that while the application is walking the pages
- * in the current window, I/O is underway on the ahead window. When the
- * current window is fully traversed, it is replaced by the ahead window
- * and the ahead window is invalidated. When this copying happens, the
- * new current window's pages are probably still locked. When I/O has
- * completed, we submit a new batch of I/O, creating a new ahead window.
- *
- * So:
- *
- * ----|----------------|----------------|-----
- * ^start ^start+size
- * ^ahead_start ^ahead_start+ahead_size
- *
- * ^ When this page is read, we submit I/O for the
- * ahead window.
- *
- * A `readahead hit' occurs when a read request is made against a page which is
- * inside the current window. Hits are good, and the window size (next_size)
- * is grown aggressively when hits occur. Two pages are added to the next
- * window size on each hit, which will end up doubling the next window size by
- * the time I/O is submitted for it.
- *
- * If readahead hits are more sparse (say, the application is only reading
- * every second page) then the window will build more slowly.
- *
- * On a readahead miss (the application seeked away) the readahead window is
- * shrunk by 25%. We don't want to drop it too aggressively, because it is a
- * good assumption that an application which has built a good readahead window
- * will continue to perform linear reads. Either at the new file position, or
- * at the old one after another seek.
- *
- * After enough misses, readahead is fully disabled. (next_size = -1UL).
- *
- * There is a special-case: if the first page which the application tries to
- * read happens to be the first page of the file, it is assumed that a linear
- * read is about to happen and the window is immediately set to half of the
- * device maximum.
- *
- * A page request at (start + size) is not a miss at all - it's just a part of
- * sequential file reading.
- *
- * This function is to be called for every page which is read, rather than when
- * it is time to perform readahead. This is so the readahead algorithm can
- * centrally work out the access patterns. This could be costly with many tiny
- * read()s, so we specifically optimise for that case with prev_page.
- */
-
-/*
- * do_page_cache_readahead actually reads a chunk of disk. It allocates all
+ * __do_page_cache_readahead() actually reads a chunk of disk. It allocates all
* the pages first, then submits them all for I/O. This avoids the very bad
* behaviour which would occur if page allocations are causing VM writeback.
* We really don't want to intermingle reads and writes like that.
*
- * Returns the number of pages which actually had IO started against them.
+ * Returns the number of pages requested, or the maximum amount of I/O allowed.
*/
-static inline int
+static int
__do_page_cache_readahead(struct address_space *mapping, struct file *filp,
- unsigned long offset, unsigned long nr_to_read)
+ pgoff_t offset, unsigned long nr_to_read,
+ unsigned long lookahead_size)
{
struct inode *inode = mapping->host;
struct page *page;
if (isize == 0)
goto out;
- end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);
+ end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);
/*
* Preallocate as many pages as we will need.
*/
- spin_lock(&mapping->page_lock);
for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
- unsigned long page_offset = offset + page_idx;
-
+ pgoff_t page_offset = offset + page_idx;
+
if (page_offset > end_index)
break;
+ rcu_read_lock();
page = radix_tree_lookup(&mapping->page_tree, page_offset);
+ rcu_read_unlock();
if (page)
continue;
- spin_unlock(&mapping->page_lock);
- page = page_cache_alloc_cold(mapping);
- spin_lock(&mapping->page_lock);
+ page = page_cache_alloc_readahead(mapping);
if (!page)
break;
page->index = page_offset;
- list_add(&page->list, &page_pool);
+ list_add(&page->lru, &page_pool);
+ if (page_idx == nr_to_read - lookahead_size)
+ SetPageReadahead(page);
ret++;
}
- spin_unlock(&mapping->page_lock);
/*
* Now start the IO. We ignore I/O errors - if the page is not
* memory at once.
*/
int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
- unsigned long offset, unsigned long nr_to_read)
+ pgoff_t offset, unsigned long nr_to_read)
{
int ret = 0;
if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
return -EINVAL;
+ nr_to_read = max_sane_readahead(nr_to_read);
while (nr_to_read) {
int err;
if (this_chunk > nr_to_read)
this_chunk = nr_to_read;
err = __do_page_cache_readahead(mapping, filp,
- offset, this_chunk);
+ offset, this_chunk, 0);
if (err < 0) {
ret = err;
break;
}
/*
- * This version skips the IO if the queue is read-congested, and will tell the
- * block layer to abandon the readahead if request allocation would block.
- *
- * force_page_cache_readahead() will ignore queue congestion and will block on
- * request queues.
+ * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
+ * sensible upper limit.
+ */
+unsigned long max_sane_readahead(unsigned long nr)
+{
+ return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE_FILE)
+ + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
+}
+
+/*
+ * Submit IO for the read-ahead request in file_ra_state.
*/
-int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
- unsigned long offset, unsigned long nr_to_read)
+unsigned long ra_submit(struct file_ra_state *ra,
+ struct address_space *mapping, struct file *filp)
{
- if (!bdi_read_congested(mapping->backing_dev_info))
- return __do_page_cache_readahead(mapping, filp,
- offset, nr_to_read);
- return 0;
+ int actual;
+
+ actual = __do_page_cache_readahead(mapping, filp,
+ ra->start, ra->size, ra->async_size);
+
+ return actual;
}
/*
- * Check how effective readahead is being. If the amount of started IO is
- * less than expected then the file is partly or fully in pagecache and
- * readahead isn't helping. Shrink the window.
+ * Set the initial window size, round to next power of 2 and square
+ * for small size, x 4 for medium, and x 2 for large
+ * for 128k (32 page) max ra
+ * 1-8 page = 32k initial, > 8 page = 128k initial
+ */
+static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
+{
+ unsigned long newsize = roundup_pow_of_two(size);
+
+ if (newsize <= max / 32)
+ newsize = newsize * 4;
+ else if (newsize <= max / 4)
+ newsize = newsize * 2;
+ else
+ newsize = max;
+
+ return newsize;
+}
+
+/*
+ * Get the previous window size, ramp it up, and
+ * return it as the new window size.
+ */
+static unsigned long get_next_ra_size(struct file_ra_state *ra,
+ unsigned long max)
+{
+ unsigned long cur = ra->size;
+ unsigned long newsize;
+
+ if (cur < max / 16)
+ newsize = 4 * cur;
+ else
+ newsize = 2 * cur;
+
+ return min(newsize, max);
+}
+
+/*
+ * On-demand readahead design.
*
- * But don't shrink it too much - the application may read the same page
- * occasionally.
+ * The fields in struct file_ra_state represent the most-recently-executed
+ * readahead attempt:
+ *
+ * |<----- async_size ---------|
+ * |------------------- size -------------------->|
+ * |==================#===========================|
+ * ^start ^page marked with PG_readahead
+ *
+ * To overlap application thinking time and disk I/O time, we do
+ * `readahead pipelining': Do not wait until the application consumed all
+ * readahead pages and stalled on the missing page at readahead_index;
+ * Instead, submit an asynchronous readahead I/O as soon as there are
+ * only async_size pages left in the readahead window. Normally async_size
+ * will be equal to size, for maximum pipelining.
+ *
+ * In interleaved sequential reads, concurrent streams on the same fd can
+ * be invalidating each other's readahead state. So we flag the new readahead
+ * page at (start+size-async_size) with PG_readahead, and use it as readahead
+ * indicator. The flag won't be set on already cached pages, to avoid the
+ * readahead-for-nothing fuss, saving pointless page cache lookups.
+ *
+ * prev_pos tracks the last visited byte in the _previous_ read request.
+ * It should be maintained by the caller, and will be used for detecting
+ * small random reads. Note that the readahead algorithm checks loosely
+ * for sequential patterns. Hence interleaved reads might be served as
+ * sequential ones.
+ *
+ * There is a special-case: if the first page which the application tries to
+ * read happens to be the first page of the file, it is assumed that a linear
+ * read is about to happen and the window is immediately set to the initial size
+ * based on I/O request size and the max_readahead.
+ *
+ * The code ramps up the readahead size aggressively at first, but slow down as
+ * it approaches max_readhead.
+ */
+
+/*
+ * Count contiguously cached pages from @offset-1 to @offset-@max,
+ * this count is a conservative estimation of
+ * - length of the sequential read sequence, or
+ * - thrashing threshold in memory tight systems
*/
-static inline void
-check_ra_success(struct file_ra_state *ra, pgoff_t attempt,
- pgoff_t actual, pgoff_t orig_next_size)
+static pgoff_t count_history_pages(struct address_space *mapping,
+ struct file_ra_state *ra,
+ pgoff_t offset, unsigned long max)
{
- if (actual == 0) {
- if (orig_next_size > 1) {
- ra->next_size = orig_next_size - 1;
- if (ra->ahead_size)
- ra->ahead_size = ra->next_size;
- } else {
- ra->next_size = -1UL;
- ra->size = 0;
- }
- }
+ pgoff_t head;
+
+ rcu_read_lock();
+ head = radix_tree_prev_hole(&mapping->page_tree, offset - 1, max);
+ rcu_read_unlock();
+
+ return offset - 1 - head;
}
/*
- * page_cache_readahead is the main function. If performs the adaptive
- * readahead window size management and submits the readahead I/O.
+ * page cache context based read-ahead
*/
-void
-page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra,
- struct file *filp, unsigned long offset)
+static int try_context_readahead(struct address_space *mapping,
+ struct file_ra_state *ra,
+ pgoff_t offset,
+ unsigned long req_size,
+ unsigned long max)
{
- unsigned max;
- unsigned min;
- unsigned orig_next_size;
- unsigned actual;
- int first_access=0;
- unsigned long preoffset=0;
+ pgoff_t size;
+
+ size = count_history_pages(mapping, ra, offset, max);
/*
- * Here we detect the case where the application is performing
- * sub-page sized reads. We avoid doing extra work and bogusly
- * perturbing the readahead window expansion logic.
- * If next_size is zero, this is the very first read for this
- * file handle, or the window is maximally shrunk.
+ * no history pages:
+ * it could be a random read
*/
- if (offset == ra->prev_page) {
- if (ra->next_size != 0)
- goto out;
- }
+ if (!size)
+ return 0;
- if (ra->next_size == -1UL)
- goto out; /* Maximally shrunk */
-
- max = get_max_readahead(ra);
- if (max == 0)
- goto out; /* No readahead */
-
- min = get_min_readahead(ra);
- orig_next_size = ra->next_size;
-
- if (ra->next_size == 0) {
- /*
- * Special case - first read.
- * We'll assume it's a whole-file read, and
- * grow the window fast.
- */
- first_access=1;
- ra->next_size = max / 2;
- goto do_io;
- }
+ /*
+ * starts from beginning of file:
+ * it is a strong indication of long-run stream (or whole-file-read)
+ */
+ if (size >= offset)
+ size *= 2;
+
+ ra->start = offset;
+ ra->size = get_init_ra_size(size + req_size, max);
+ ra->async_size = ra->size;
+
+ return 1;
+}
- preoffset = ra->prev_page;
- ra->prev_page = offset;
-
- if (offset >= ra->start && offset <= (ra->start + ra->size)) {
- /*
- * A readahead hit. Either inside the window, or one
- * page beyond the end. Expand the next readahead size.
- */
- ra->next_size += 2;
- } else {
- /*
- * A miss - lseek, pagefault, pread, etc. Shrink the readahead
- * window.
- */
- ra->next_size -= 2;
+/*
+ * A minimal readahead algorithm for trivial sequential/random reads.
+ */
+static unsigned long
+ondemand_readahead(struct address_space *mapping,
+ struct file_ra_state *ra, struct file *filp,
+ bool hit_readahead_marker, pgoff_t offset,
+ unsigned long req_size)
+{
+ unsigned long max = max_sane_readahead(ra->ra_pages);
+
+ /*
+ * start of file
+ */
+ if (!offset)
+ goto initial_readahead;
+
+ /*
+ * It's the expected callback offset, assume sequential access.
+ * Ramp up sizes, and push forward the readahead window.
+ */
+ if ((offset == (ra->start + ra->size - ra->async_size) ||
+ offset == (ra->start + ra->size))) {
+ ra->start += ra->size;
+ ra->size = get_next_ra_size(ra, max);
+ ra->async_size = ra->size;
+ goto readit;
}
- if ((long)ra->next_size > (long)max)
- ra->next_size = max;
- if ((long)ra->next_size <= 0L) {
- ra->next_size = -1UL;
- ra->size = 0;
- goto out; /* Readahead is off */
+ /*
+ * Hit a marked page without valid readahead state.
+ * E.g. interleaved reads.
+ * Query the pagecache for async_size, which normally equals to
+ * readahead size. Ramp it up and use it as the new readahead size.
+ */
+ if (hit_readahead_marker) {
+ pgoff_t start;
+
+ rcu_read_lock();
+ start = radix_tree_next_hole(&mapping->page_tree, offset+1,max);
+ rcu_read_unlock();
+
+ if (!start || start - offset > max)
+ return 0;
+
+ ra->start = start;
+ ra->size = start - offset; /* old async_size */
+ ra->size += req_size;
+ ra->size = get_next_ra_size(ra, max);
+ ra->async_size = ra->size;
+ goto readit;
}
/*
- * Is this request outside the current window?
+ * oversize read
*/
- if (offset < ra->start || offset >= (ra->start + ra->size)) {
- /*
- * A miss against the current window. Have we merely
- * advanced into the ahead window?
- */
- if (offset == ra->ahead_start) {
- /*
- * Yes, we have. The ahead window now becomes
- * the current window.
- */
- ra->start = ra->ahead_start;
- ra->size = ra->ahead_size;
- ra->prev_page = ra->start;
- ra->ahead_start = 0;
- ra->ahead_size = 0;
-
- /*
- * Control now returns, probably to sleep until I/O
- * completes against the first ahead page.
- * When the second page in the old ahead window is
- * requested, control will return here and more I/O
- * will be submitted to build the new ahead window.
- */
- goto out;
- }
-do_io:
- /*
- * This is the "unusual" path. We come here during
- * startup or after an lseek. We invalidate the
- * ahead window and get some I/O underway for the new
- * current window.
- */
- if (!first_access && preoffset >= ra->start &&
- preoffset < (ra->start + ra->size)) {
- /* Heuristic: If 'n' pages were
- * accessed in the current window, there
- * is a high probability that around 'n' pages
- * shall be used in the next current window.
- */
- ra->next_size = preoffset - ra->start + 1;
- }
- ra->start = offset;
- ra->size = ra->next_size;
- ra->ahead_start = 0; /* Invalidate these */
- ra->ahead_size = 0;
- actual = do_page_cache_readahead(mapping, filp, offset,
- ra->size);
- if(!first_access) {
- /*
- * do not adjust the readahead window size the first
- * time, the ahead window might get closed if all
- * the pages are already in the cache.
- */
- check_ra_success(ra, ra->size, actual, orig_next_size);
- }
- } else {
- /*
- * This read request is within the current window. It is time
- * to submit I/O for the ahead window while the application is
- * crunching through the current window.
- */
- if (ra->ahead_start == 0) {
- ra->ahead_start = ra->start + ra->size;
- ra->ahead_size = ra->next_size;
- actual = do_page_cache_readahead(mapping, filp,
- ra->ahead_start, ra->ahead_size);
- check_ra_success(ra, ra->ahead_size,
- actual, orig_next_size);
- }
+ if (req_size > max)
+ goto initial_readahead;
+
+ /*
+ * sequential cache miss
+ */
+ if (offset - (ra->prev_pos >> PAGE_CACHE_SHIFT) <= 1UL)
+ goto initial_readahead;
+
+ /*
+ * Query the page cache and look for the traces(cached history pages)
+ * that a sequential stream would leave behind.
+ */
+ if (try_context_readahead(mapping, ra, offset, req_size, max))
+ goto readit;
+
+ /*
+ * standalone, small random read
+ * Read as is, and do not pollute the readahead state.
+ */
+ return __do_page_cache_readahead(mapping, filp, offset, req_size, 0);
+
+initial_readahead:
+ ra->start = offset;
+ ra->size = get_init_ra_size(req_size, max);
+ ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
+
+readit:
+ /*
+ * Will this read hit the readahead marker made by itself?
+ * If so, trigger the readahead marker hit now, and merge
+ * the resulted next readahead window into the current one.
+ */
+ if (offset == ra->start && ra->size == ra->async_size) {
+ ra->async_size = get_next_ra_size(ra, max);
+ ra->size += ra->async_size;
}
-out:
- return;
-}
+ return ra_submit(ra, mapping, filp);
+}
-/*
- * handle_ra_miss() is called when it is known that a page which should have
- * been present in the pagecache (we just did some readahead there) was in fact
- * not found. This will happen if it was evicted by the VM (readahead
- * thrashing) or if the readahead window is maximally shrunk.
- *
- * If the window has been maximally shrunk (next_size == -1UL) then look to see
- * if we are getting misses against sequential file offsets. If so, and this
- * persists then resume readahead.
+/**
+ * page_cache_sync_readahead - generic file readahead
+ * @mapping: address_space which holds the pagecache and I/O vectors
+ * @ra: file_ra_state which holds the readahead state
+ * @filp: passed on to ->readpage() and ->readpages()
+ * @offset: start offset into @mapping, in pagecache page-sized units
+ * @req_size: hint: total size of the read which the caller is performing in
+ * pagecache pages
*
- * Otherwise we're thrashing, so shrink the readahead window by three pages.
- * This is because it is grown by two pages on a readahead hit. Theory being
- * that the readahead window size will stabilise around the maximum level at
- * which there is no thrashing.
+ * page_cache_sync_readahead() should be called when a cache miss happened:
+ * it will submit the read. The readahead logic may decide to piggyback more
+ * pages onto the read request if access patterns suggest it will improve
+ * performance.
*/
-void handle_ra_miss(struct address_space *mapping,
- struct file_ra_state *ra, pgoff_t offset)
+void page_cache_sync_readahead(struct address_space *mapping,
+ struct file_ra_state *ra, struct file *filp,
+ pgoff_t offset, unsigned long req_size)
{
- if (ra->next_size == -1UL) {
- const unsigned long max = get_max_readahead(ra);
-
- if (offset != ra->prev_page + 1) {
- ra->size = ra->size?ra->size-1:0; /* Not sequential */
- } else {
- ra->size++; /* A sequential read */
- if (ra->size >= max) { /* Resume readahead */
- ra->start = offset - max;
- ra->next_size = max;
- ra->size = max;
- ra->ahead_start = 0;
- ra->ahead_size = 0;
- }
- }
- ra->prev_page = offset;
- } else {
- const unsigned long min = get_min_readahead(ra);
-
- ra->next_size -= 3;
- if (ra->next_size < min)
- ra->next_size = min;
+ /* no read-ahead */
+ if (!ra->ra_pages)
+ return;
+
+ /* be dumb */
+ if (filp && (filp->f_mode & FMODE_RANDOM)) {
+ force_page_cache_readahead(mapping, filp, offset, req_size);
+ return;
}
+
+ /* do read-ahead */
+ ondemand_readahead(mapping, ra, filp, false, offset, req_size);
}
+EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
-/*
- * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
- * sensible upper limit.
+/**
+ * page_cache_async_readahead - file readahead for marked pages
+ * @mapping: address_space which holds the pagecache and I/O vectors
+ * @ra: file_ra_state which holds the readahead state
+ * @filp: passed on to ->readpage() and ->readpages()
+ * @page: the page at @offset which has the PG_readahead flag set
+ * @offset: start offset into @mapping, in pagecache page-sized units
+ * @req_size: hint: total size of the read which the caller is performing in
+ * pagecache pages
+ *
+ * page_cache_async_readahead() should be called when a page is used which
+ * has the PG_readahead flag; this is a marker to suggest that the application
+ * has used up enough of the readahead window that we should start pulling in
+ * more pages.
*/
-unsigned long max_sane_readahead(unsigned long nr)
+void
+page_cache_async_readahead(struct address_space *mapping,
+ struct file_ra_state *ra, struct file *filp,
+ struct page *page, pgoff_t offset,
+ unsigned long req_size)
{
- unsigned long active;
- unsigned long inactive;
- unsigned long free;
+ /* no read-ahead */
+ if (!ra->ra_pages)
+ return;
+
+ /*
+ * Same bit is used for PG_readahead and PG_reclaim.
+ */
+ if (PageWriteback(page))
+ return;
+
+ ClearPageReadahead(page);
+
+ /*
+ * Defer asynchronous read-ahead on IO congestion.
+ */
+ if (bdi_read_congested(mapping->backing_dev_info))
+ return;
- get_zone_counts(&active, &inactive, &free);
- return min(nr, (inactive + free) / 2);
+ /* do read-ahead */
+ ondemand_readahead(mapping, ra, filp, true, offset, req_size);
}
+EXPORT_SYMBOL_GPL(page_cache_async_readahead);
projects / linux-flexiantxendom0-3.2.10.git / blobdiff