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Subject[PATCH 24/30] FS-Cache: Release page->private in failed readahead [try #11]
Date
The attached patch causes read_cache_pages() to release page-private data on a
page for which add_to_page_cache() fails or the filler function fails. This
permits pages with caching references associated with them to be cleaned up.

Further changes [try #9] that have been made:

(*) The try_to_release_page() is called instead of calling the releasepage()
op directly.

(*) The page is locked before try_to_release_page() is called.

(*) The call to try_to_release_page() and page_cache_release() have been
abstracted out into a helper function as this bit of code occurs twice..

Further changes [try #10] that have been made:

(*) The comment header on the helper function is much expanded. This states
why there's a need to call the releasepage() op in the event of an error.

(*) BUG() if the page is already locked when we try and lock it.

(*) Don't set the page mapping pointer until we've locked the page.

(*) The page is unlocked after try_to_release_page() is called.

Signed-Off-By: David Howells <dhowells@redhat.com>
---

mm/readahead.c | 25 +++++++++++++++++++++++--
1 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index aa7ec42..54d3393 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -14,6 +14,7 @@ #include <linux/module.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
+#include <linux/buffer_head.h>

void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
{
@@ -117,6 +118,26 @@ static inline unsigned long get_next_ra_

#define list_to_page(head) (list_entry((head)->prev, struct page, lru))

+/*
+ * see if a page needs releasing upon read_cache_pages() failure
+ * - the caller of read_cache_pages() may have set PG_private 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_release_page(struct address_space *mapping,
+ struct page *page)
+{
+ if (PagePrivate(page)) {
+ if (TestSetPageLocked(page))
+ BUG();
+ page->mapping = mapping;
+ try_to_release_page(page, GFP_KERNEL);
+ page->mapping = NULL;
+ unlock_page(page);
+ }
+ page_cache_release(page);
+}
+
/**
* read_cache_pages - populate an address space with some pages & start reads against them
* @mapping: the address_space
@@ -140,7 +161,7 @@ int read_cache_pages(struct address_spac
page = list_to_page(pages);
list_del(&page->lru);
if (add_to_page_cache(page, mapping, page->index, GFP_KERNEL)) {
- page_cache_release(page);
+ read_cache_pages_release_page(mapping, page);
continue;
}
ret = filler(data, page);
@@ -152,7 +173,7 @@ int read_cache_pages(struct address_spac

victim = list_to_page(pages);
list_del(&victim->lru);
- page_cache_release(victim);
+ read_cache_pages_release_page(mapping, victim);
}
break;
}
-
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