#include <linux/mm_inline.h>
#include <linux/blk-cgroup.h>
#include <linux/fadvise.h>
+#include <linux/sched/mm.h>
#include "internal.h"
EXPORT_SYMBOL(read_cache_pages);
-static int read_pages(struct address_space *mapping, struct file *filp,
- struct list_head *pages, unsigned int nr_pages, gfp_t gfp)
+static void read_pages(struct readahead_control *rac, struct list_head *pages,
+ bool skip_page)
{
+ const struct address_space_operations *aops = rac->mapping->a_ops;
+ struct page *page;
struct blk_plug plug;
- unsigned page_idx;
- int ret;
+
+ if (!readahead_count(rac))
+ goto out;
blk_start_plug(&plug);
- if (mapping->a_ops->readpages) {
- ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
+ if (aops->readahead) {
+ aops->readahead(rac);
+ /* Clean up the remaining pages */
+ while ((page = readahead_page(rac))) {
+ unlock_page(page);
+ put_page(page);
+ }
+ } else if (aops->readpages) {
+ aops->readpages(rac->file, rac->mapping, pages,
+ readahead_count(rac));
/* Clean up the remaining pages */
put_pages_list(pages);
- goto out;
- }
-
- for (page_idx = 0; page_idx < nr_pages; page_idx++) {
- struct page *page = lru_to_page(pages);
- list_del(&page->lru);
- if (!add_to_page_cache_lru(page, mapping, page->index, gfp))
- mapping->a_ops->readpage(filp, page);
- put_page(page);
+ rac->_index += rac->_nr_pages;
+ rac->_nr_pages = 0;
+ } else {
+ while ((page = readahead_page(rac))) {
+ aops->readpage(rac->file, page);
+ put_page(page);
+ }
}
- ret = 0;
-out:
blk_finish_plug(&plug);
- return ret;
+ BUG_ON(!list_empty(pages));
+ BUG_ON(readahead_count(rac));
+
+out:
+ if (skip_page)
+ rac->_index++;
}
-/*
- * __do_page_cache_readahead() actually reads a chunk of disk. It allocates
- * the pages first, then submits them 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.
+/**
+ * page_cache_readahead_unbounded - Start unchecked readahead.
+ * @mapping: File address space.
+ * @file: This instance of the open file; used for authentication.
+ * @index: First page index to read.
+ * @nr_to_read: The number of pages to read.
+ * @lookahead_size: Where to start the next readahead.
*
- * Returns the number of pages requested, or the maximum amount of I/O allowed.
+ * This function is for filesystems to call when they want to start
+ * readahead beyond a file's stated i_size. This is almost certainly
+ * not the function you want to call. Use page_cache_async_readahead()
+ * or page_cache_sync_readahead() instead.
+ *
+ * Context: File is referenced by caller. Mutexes may be held by caller.
+ * May sleep, but will not reenter filesystem to reclaim memory.
*/
-unsigned int __do_page_cache_readahead(struct address_space *mapping,
- struct file *filp, pgoff_t offset, unsigned long nr_to_read,
+void page_cache_readahead_unbounded(struct address_space *mapping,
+ struct file *file, pgoff_t index, unsigned long nr_to_read,
unsigned long lookahead_size)
{
- struct inode *inode = mapping->host;
- struct page *page;
- unsigned long end_index; /* The last page we want to read */
LIST_HEAD(page_pool);
- int page_idx;
- unsigned int nr_pages = 0;
- loff_t isize = i_size_read(inode);
gfp_t gfp_mask = readahead_gfp_mask(mapping);
+ struct readahead_control rac = {
+ .mapping = mapping,
+ .file = file,
+ ._index = index,
+ };
+ unsigned long i;
- if (isize == 0)
- goto out;
-
- end_index = ((isize - 1) >> PAGE_SHIFT);
+ /*
+ * Partway through the readahead operation, we will have added
+ * locked pages to the page cache, but will not yet have submitted
+ * them for I/O. Adding another page may need to allocate memory,
+ * which can trigger memory reclaim. Telling the VM we're in
+ * the middle of a filesystem operation will cause it to not
+ * touch file-backed pages, preventing a deadlock. Most (all?)
+ * filesystems already specify __GFP_NOFS in their mapping's
+ * gfp_mask, but let's be explicit here.
+ */
+ unsigned int nofs = memalloc_nofs_save();
/*
* Preallocate as many pages as we will need.
*/
- for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
- pgoff_t page_offset = offset + page_idx;
+ for (i = 0; i < nr_to_read; i++) {
+ struct page *page = xa_load(&mapping->i_pages, index + i);
- if (page_offset > end_index)
- break;
+ BUG_ON(index + i != rac._index + rac._nr_pages);
- page = xa_load(&mapping->i_pages, page_offset);
if (page && !xa_is_value(page)) {
/*
- * Page already present? Kick off the current batch of
- * contiguous pages before continuing with the next
- * batch.
+ * Page already present? Kick off the current batch
+ * of contiguous pages before continuing with the
+ * next batch. This page may be the one we would
+ * have intended to mark as Readahead, but we don't
+ * have a stable reference to this page, and it's
+ * not worth getting one just for that.
*/
- if (nr_pages)
- read_pages(mapping, filp, &page_pool, nr_pages,
- gfp_mask);
- nr_pages = 0;
+ read_pages(&rac, &page_pool, true);
continue;
}
page = __page_cache_alloc(gfp_mask);
if (!page)
break;
- page->index = page_offset;
- list_add(&page->lru, &page_pool);
- if (page_idx == nr_to_read - lookahead_size)
+ if (mapping->a_ops->readpages) {
+ page->index = index + i;
+ list_add(&page->lru, &page_pool);
+ } else if (add_to_page_cache_lru(page, mapping, index + i,
+ gfp_mask) < 0) {
+ put_page(page);
+ read_pages(&rac, &page_pool, true);
+ continue;
+ }
+ if (i == nr_to_read - lookahead_size)
SetPageReadahead(page);
- nr_pages++;
+ rac._nr_pages++;
}
/*
* uptodate then the caller will launch readpage again, and
* will then handle the error.
*/
- if (nr_pages)
- read_pages(mapping, filp, &page_pool, nr_pages, gfp_mask);
- BUG_ON(!list_empty(&page_pool));
-out:
- return nr_pages;
+ read_pages(&rac, &page_pool, false);
+ memalloc_nofs_restore(nofs);
+}
+EXPORT_SYMBOL_GPL(page_cache_readahead_unbounded);
+
+/*
+ * __do_page_cache_readahead() actually reads a chunk of disk. It allocates
+ * the pages first, then submits them 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.
+ */
+void __do_page_cache_readahead(struct address_space *mapping,
+ struct file *file, pgoff_t index, unsigned long nr_to_read,
+ unsigned long lookahead_size)
+{
+ struct inode *inode = mapping->host;
+ loff_t isize = i_size_read(inode);
+ pgoff_t end_index; /* The last page we want to read */
+
+ if (isize == 0)
+ return;
+
+ end_index = (isize - 1) >> PAGE_SHIFT;
+ if (index > end_index)
+ return;
+ /* Don't read past the page containing the last byte of the file */
+ if (nr_to_read > end_index - index)
+ nr_to_read = end_index - index + 1;
+
+ page_cache_readahead_unbounded(mapping, file, index, nr_to_read,
+ lookahead_size);
}
/*
* Chunk the readahead into 2 megabyte units, so that we don't pin too much
* memory at once.
*/
-int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
- pgoff_t offset, unsigned long nr_to_read)
+void force_page_cache_readahead(struct address_space *mapping,
+ struct file *filp, pgoff_t index, unsigned long nr_to_read)
{
struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
struct file_ra_state *ra = &filp->f_ra;
unsigned long max_pages;
- if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
- return -EINVAL;
+ if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages &&
+ !mapping->a_ops->readahead))
+ return;
/*
* If the request exceeds the readahead window, allow the read to
if (this_chunk > nr_to_read)
this_chunk = nr_to_read;
- __do_page_cache_readahead(mapping, filp, offset, this_chunk, 0);
+ __do_page_cache_readahead(mapping, filp, index, this_chunk, 0);
- offset += this_chunk;
+ index += this_chunk;
nr_to_read -= this_chunk;
}
- return 0;
}
/*
*/
/*
- * Count contiguously cached pages from @offset-1 to @offset-@max,
+ * Count contiguously cached pages from @index-1 to @index-@max,
* this count is a conservative estimation of
* - length of the sequential read sequence, or
* - thrashing threshold in memory tight systems
*/
static pgoff_t count_history_pages(struct address_space *mapping,
- pgoff_t offset, unsigned long max)
+ pgoff_t index, unsigned long max)
{
pgoff_t head;
rcu_read_lock();
- head = page_cache_prev_miss(mapping, offset - 1, max);
+ head = page_cache_prev_miss(mapping, index - 1, max);
rcu_read_unlock();
- return offset - 1 - head;
+ return index - 1 - head;
}
/*
*/
static int try_context_readahead(struct address_space *mapping,
struct file_ra_state *ra,
- pgoff_t offset,
+ pgoff_t index,
unsigned long req_size,
unsigned long max)
{
pgoff_t size;
- size = count_history_pages(mapping, offset, max);
+ size = count_history_pages(mapping, index, max);
/*
* not enough history pages:
* starts from beginning of file:
* it is a strong indication of long-run stream (or whole-file-read)
*/
- if (size >= offset)
+ if (size >= index)
size *= 2;
- ra->start = offset;
+ ra->start = index;
ra->size = min(size + req_size, max);
ra->async_size = 1;
/*
* 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)
+static void ondemand_readahead(struct address_space *mapping,
+ struct file_ra_state *ra, struct file *filp,
+ bool hit_readahead_marker, pgoff_t index,
+ unsigned long req_size)
{
struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
unsigned long max_pages = ra->ra_pages;
unsigned long add_pages;
- pgoff_t prev_offset;
+ pgoff_t prev_index;
/*
* If the request exceeds the readahead window, allow the read to
/*
* start of file
*/
- if (!offset)
+ if (!index)
goto initial_readahead;
/*
- * It's the expected callback offset, assume sequential access.
+ * It's the expected callback index, 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))) {
+ if ((index == (ra->start + ra->size - ra->async_size) ||
+ index == (ra->start + ra->size))) {
ra->start += ra->size;
ra->size = get_next_ra_size(ra, max_pages);
ra->async_size = ra->size;
pgoff_t start;
rcu_read_lock();
- start = page_cache_next_miss(mapping, offset + 1, max_pages);
+ start = page_cache_next_miss(mapping, index + 1, max_pages);
rcu_read_unlock();
- if (!start || start - offset > max_pages)
- return 0;
+ if (!start || start - index > max_pages)
+ return;
ra->start = start;
- ra->size = start - offset; /* old async_size */
+ ra->size = start - index; /* old async_size */
ra->size += req_size;
ra->size = get_next_ra_size(ra, max_pages);
ra->async_size = ra->size;
/*
* sequential cache miss
- * trivial case: (offset - prev_offset) == 1
- * unaligned reads: (offset - prev_offset) == 0
+ * trivial case: (index - prev_index) == 1
+ * unaligned reads: (index - prev_index) == 0
*/
- prev_offset = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
- if (offset - prev_offset <= 1UL)
+ prev_index = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
+ if (index - prev_index <= 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_pages))
+ if (try_context_readahead(mapping, ra, index, req_size, max_pages))
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);
+ __do_page_cache_readahead(mapping, filp, index, req_size, 0);
+ return;
initial_readahead:
- ra->start = offset;
+ ra->start = index;
ra->size = get_init_ra_size(req_size, max_pages);
ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
* the resulted next readahead window into the current one.
* Take care of maximum IO pages as above.
*/
- if (offset == ra->start && ra->size == ra->async_size) {
+ if (index == ra->start && ra->size == ra->async_size) {
add_pages = get_next_ra_size(ra, max_pages);
if (ra->size + add_pages <= max_pages) {
ra->async_size = add_pages;
}
}
- return ra_submit(ra, mapping, filp);
+ ra_submit(ra, mapping, filp);
}
/**
* @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
+ * @index: Index of first page to be read.
+ * @req_count: Total number of pages being read by the caller.
*
* 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
*/
void page_cache_sync_readahead(struct address_space *mapping,
struct file_ra_state *ra, struct file *filp,
- pgoff_t offset, unsigned long req_size)
+ pgoff_t index, unsigned long req_count)
{
/* no read-ahead */
if (!ra->ra_pages)
/* be dumb */
if (filp && (filp->f_mode & FMODE_RANDOM)) {
- force_page_cache_readahead(mapping, filp, offset, req_size);
+ force_page_cache_readahead(mapping, filp, index, req_count);
return;
}
/* do read-ahead */
- ondemand_readahead(mapping, ra, filp, false, offset, req_size);
+ ondemand_readahead(mapping, ra, filp, false, index, req_count);
}
EXPORT_SYMBOL_GPL(page_cache_sync_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()
- * @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: The page at @index which triggered the readahead call.
+ * @index: Index of first page to be read.
+ * @req_count: Total number of pages being read by the caller.
*
* 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
+ * is marked as PageReadahead; 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.
*/
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)
+ struct page *page, pgoff_t index,
+ unsigned long req_count)
{
/* no read-ahead */
if (!ra->ra_pages)
return;
/* do read-ahead */
- ondemand_readahead(mapping, ra, filp, true, offset, req_size);
+ ondemand_readahead(mapping, ra, filp, true, index, req_count);
}
EXPORT_SYMBOL_GPL(page_cache_async_readahead);
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