*
* Readahead is used to read content into the page cache before it is
* explicitly requested by the application. Readahead only ever
- * attempts to read pages that are not yet in the page cache. If a
- * page is present but not up-to-date, readahead will not try to read
+ * attempts to read folios that are not yet in the page cache. If a
+ * folio is present but not up-to-date, readahead will not try to read
* it. In that case a simple ->readpage() will be requested.
*
* Readahead is triggered when an application read request (whether a
- * systemcall or a page fault) finds that the requested page is not in
+ * system call or a page fault) finds that the requested folio is not in
* the page cache, or that it is in the page cache and has the
- * %PG_readahead flag set. This flag indicates that the page was loaded
- * as part of a previous read-ahead request and now that it has been
- * accessed, it is time for the next read-ahead.
+ * readahead flag set. This flag indicates that the folio was read
+ * as part of a previous readahead request and now that it has been
+ * accessed, it is time for the next readahead.
*
* Each readahead request is partly synchronous read, and partly async
- * read-ahead. This is reflected in the struct file_ra_state which
- * contains ->size being to total number of pages, and ->async_size
- * which is the number of pages in the async section. The first page in
- * this async section will have %PG_readahead set as a trigger for a
- * subsequent read ahead. Once a series of sequential reads has been
+ * readahead. This is reflected in the struct file_ra_state which
+ * contains ->size being the total number of pages, and ->async_size
+ * which is the number of pages in the async section. The readahead
+ * flag will be set on the first folio in this async section to trigger
+ * a subsequent readahead. Once a series of sequential reads has been
* established, there should be no need for a synchronous component and
- * all read ahead request will be fully asynchronous.
+ * all readahead request will be fully asynchronous.
*
- * When either of the triggers causes a readahead, three numbers need to
- * be determined: the start of the region, the size of the region, and
- * the size of the async tail.
+ * When either of the triggers causes a readahead, three numbers need
+ * to be determined: the start of the region to read, the size of the
+ * region, and the size of the async tail.
*
* The start of the region is simply the first page address at or after
* the accessed address, which is not currently populated in the page
* was explicitly requested from the determined request size, unless
* this would be less than zero - then zero is used. NOTE THIS
* CALCULATION IS WRONG WHEN THE START OF THE REGION IS NOT THE ACCESSED
- * PAGE.
+ * PAGE. ALSO THIS CALCULATION IS NOT USED CONSISTENTLY.
*
* The size of the region is normally determined from the size of the
* previous readahead which loaded the preceding pages. This may be
* discovered from the struct file_ra_state for simple sequential reads,
* or from examining the state of the page cache when multiple
* sequential reads are interleaved. Specifically: where the readahead
- * was triggered by the %PG_readahead flag, the size of the previous
+ * was triggered by the readahead flag, the size of the previous
* readahead is assumed to be the number of pages from the triggering
* page to the start of the new readahead. In these cases, the size of
* the previous readahead is scaled, often doubled, for the new
* larger than the current request, and it is not scaled up, unless it
* is at the start of file.
*
- * In general read ahead is accelerated at the start of the file, as
+ * In general readahead is accelerated at the start of the file, as
* reads from there are often sequential. There are other minor
- * adjustments to the read ahead size in various special cases and these
+ * adjustments to the readahead size in various special cases and these
* are best discovered by reading the code.
*
- * The above calculation determines the readahead, to which any requested
- * read size may be added.
+ * The above calculation, based on the previous readahead size,
+ * determines the size of the readahead, to which any requested read
+ * size may be added.
*
* Readahead requests are sent to the filesystem using the ->readahead()
* address space operation, for which mpage_readahead() is a canonical
* implementation. ->readahead() should normally initiate reads on all
- * pages, but may fail to read any or all pages without causing an IO
+ * folios, but may fail to read any or all folios without causing an I/O
* error. The page cache reading code will issue a ->readpage() request
- * for any page which ->readahead() does not provided, and only an error
+ * for any folio which ->readahead() did not read, and only an error
* from this will be final.
*
- * ->readahead() will generally call readahead_page() repeatedly to get
- * each page from those prepared for read ahead. It may fail to read a
- * page by:
+ * ->readahead() will generally call readahead_folio() repeatedly to get
+ * each folio from those prepared for readahead. It may fail to read a
+ * folio by:
*
- * * not calling readahead_page() sufficiently many times, effectively
- * ignoring some pages, as might be appropriate if the path to
+ * * not calling readahead_folio() sufficiently many times, effectively
+ * ignoring some folios, as might be appropriate if the path to
* storage is congested.
*
- * * failing to actually submit a read request for a given page,
+ * * failing to actually submit a read request for a given folio,
* possibly due to insufficient resources, or
*
* * getting an error during subsequent processing of a request.
*
- * In the last two cases, the page should be unlocked to indicate that
- * the read attempt has failed. In the first case the page will be
- * unlocked by the caller.
+ * In the last two cases, the folio should be unlocked by the filesystem
+ * to indicate that the read attempt has failed. In the first case the
+ * folio will be unlocked by the VFS.
*
- * Those pages not in the final ``async_size`` of the request should be
+ * Those folios not in the final ``async_size`` of the request should be
* considered to be important and ->readahead() should not fail them due
* to congestion or temporary resource unavailability, but should wait
* for necessary resources (e.g. memory or indexing information) to
- * become available. Pages in the final ``async_size`` may be
+ * become available. Folios in the final ``async_size`` may be
* considered less urgent and failure to read them is more acceptable.
- * In this case it is best to use delete_from_page_cache() to remove the
- * pages from the page cache as is automatically done for pages that
- * were not fetched with readahead_page(). This will allow a
- * subsequent synchronous read ahead request to try them again. If they
+ * In this case it is best to use filemap_remove_folio() to remove the
+ * folios from the page cache as is automatically done for folios that
+ * were not fetched with readahead_folio(). This will allow a
+ * subsequent synchronous readahead request to try them again. If they
* are left in the page cache, then they will be read individually using
- * ->readpage().
- *
+ * ->readpage() which may be less efficient.
*/
#include <linux/kernel.h>
}
EXPORT_SYMBOL_GPL(file_ra_state_init);
-/*
- * 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 void read_cache_pages_invalidate_page(struct address_space *mapping,
- struct page *page)
-{
- if (page_has_private(page)) {
- if (!trylock_page(page))
- BUG();
- page->mapping = mapping;
- folio_invalidate(page_folio(page), 0, PAGE_SIZE);
- page->mapping = NULL;
- unlock_page(page);
- }
- put_page(page);
-}
-
-/*
- * 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)
-{
- struct page *victim;
-
- while (!list_empty(pages)) {
- victim = lru_to_page(pages);
- list_del(&victim->lru);
- read_cache_pages_invalidate_page(mapping, victim);
- }
-}
-
-/**
- * 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.
- * @filler: callback routine for filling a single page.
- * @data: private data for the callback routine.
- *
- * Hides the details of the LRU cache etc from the filesystems.
- *
- * Returns: %0 on success, error return by @filler otherwise
- */
-int read_cache_pages(struct address_space *mapping, struct list_head *pages,
- int (*filler)(void *, struct page *), void *data)
-{
- struct page *page;
- int ret = 0;
-
- while (!list_empty(pages)) {
- page = lru_to_page(pages);
- list_del(&page->lru);
- if (add_to_page_cache_lru(page, mapping, page->index,
- readahead_gfp_mask(mapping))) {
- read_cache_pages_invalidate_page(mapping, page);
- continue;
- }
- put_page(page);
-
- ret = filler(data, page);
- if (unlikely(ret)) {
- read_cache_pages_invalidate_pages(mapping, pages);
- break;
- }
- task_io_account_read(PAGE_SIZE);
- }
- return ret;
-}
-
-EXPORT_SYMBOL(read_cache_pages);
-
-static void read_pages(struct readahead_control *rac, struct list_head *pages,
- bool skip_page)
+static void read_pages(struct readahead_control *rac)
{
const struct address_space_operations *aops = rac->mapping->a_ops;
struct page *page;
struct blk_plug plug;
if (!readahead_count(rac))
- goto out;
+ return;
blk_start_plug(&plug);
aops->readahead(rac);
/*
* Clean up the remaining pages. The sizes in ->ra
- * maybe be used to size next read-ahead, so make sure
+ * may be used to size the next readahead, so make sure
* they accurately reflect what happened.
*/
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);
- rac->_index += rac->_nr_pages;
- rac->_nr_pages = 0;
} else {
while ((page = readahead_page(rac))) {
aops->readpage(rac->file, page);
blk_finish_plug(&plug);
- BUG_ON(pages && !list_empty(pages));
BUG_ON(readahead_count(rac));
-
-out:
- if (skip_page)
- rac->_index++;
}
/**
{
struct address_space *mapping = ractl->mapping;
unsigned long index = readahead_index(ractl);
- LIST_HEAD(page_pool);
gfp_t gfp_mask = readahead_gfp_mask(mapping);
unsigned long i;
* have a stable reference to this page, and it's
* not worth getting one just for that.
*/
- read_pages(ractl, &page_pool, true);
+ read_pages(ractl);
+ ractl->_index++;
i = ractl->_index + ractl->_nr_pages - index - 1;
continue;
}
folio = filemap_alloc_folio(gfp_mask, 0);
if (!folio)
break;
- if (mapping->a_ops->readpages) {
- folio->index = index + i;
- list_add(&folio->lru, &page_pool);
- } else if (filemap_add_folio(mapping, folio, index + i,
+ if (filemap_add_folio(mapping, folio, index + i,
gfp_mask) < 0) {
folio_put(folio);
- read_pages(ractl, &page_pool, true);
+ read_pages(ractl);
+ ractl->_index++;
i = ractl->_index + ractl->_nr_pages - index - 1;
continue;
}
* uptodate then the caller will launch readpage again, and
* will then handle the error.
*/
- read_pages(ractl, &page_pool, false);
+ read_pages(ractl);
filemap_invalidate_unlock_shared(mapping);
memalloc_nofs_restore(nofs);
}
struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
unsigned long max_pages, index;
- if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages &&
- !mapping->a_ops->readahead))
+ if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readahead))
return;
/*
}
/*
- * page cache context based read-ahead
+ * page cache context based readahead
*/
static int try_context_readahead(struct address_space *mapping,
struct file_ra_state *ra,
ra->async_size += index - limit - 1;
}
- read_pages(ractl, NULL, false);
+ read_pages(ractl);
/*
* If there were already pages in the page cache, then we may have
bool do_forced_ra = ractl->file && (ractl->file->f_mode & FMODE_RANDOM);
/*
- * Even if read-ahead is disabled, issue this request as read-ahead
+ * Even if readahead is disabled, issue this request as readahead
* as we'll need it to satisfy the requested range. The forced
- * read-ahead will do the right thing and limit the read to just the
+ * readahead will do the right thing and limit the read to just the
* requested range, which we'll set to 1 page for this case.
*/
if (!ractl->ra->ra_pages || blk_cgroup_congested()) {
return;
}
- /* do read-ahead */
ondemand_readahead(ractl, NULL, req_count);
}
EXPORT_SYMBOL_GPL(page_cache_sync_ra);
void page_cache_async_ra(struct readahead_control *ractl,
struct folio *folio, unsigned long req_count)
{
- /* no read-ahead */
+ /* no readahead */
if (!ractl->ra->ra_pages)
return;
if (blk_cgroup_congested())
return;
- /* do read-ahead */
ondemand_readahead(ractl, folio, req_count);
}
EXPORT_SYMBOL_GPL(page_cache_async_ra);
projects / linux-2.6-microblaze.git / blobdiff