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Subject[PATCH] AOP_TRUNCATED_PAGE victims in read_pages() belong in the LRU
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AOP_TRUNCATED_PAGE victims in read_pages() belong in the LRU

Nick Piggin rightly pointed out that the introduction of AOP_TRUNCATED_PAGE to
read_pages() was wrong to leave A_T_P victim pages in the page cache but not
put them in the LRU. Failing to do so hid them from the VM.

A_T_P just means that the aop method unlocked the page rather than performing
IO. It would be very rare that the page was truncated between the unlock and
testing A_T_P. So we leave the pages in the LRU for likely reuse soon rather
than backing them back out of the page cache. We do this by matching the
behaviour before the A_T_P introduction which added pages to the LRU regardless
of what ->readpage() did.

This doesn't include the unrelated cleanup in Nick's initial fix which changed
read_pages() to return void to match its only caller's behaviour of ignoring
errors.

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Zach Brown <zach.brown@oracle.com>
---
mm/readahead.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
Index: 2.6.17-rc3-git7-read_pages-fix/mm/readahead.c
===================================================================
--- 2.6.17-rc3-git7-read_pages-fix.orig/mm/readahead.c
+++ 2.6.17-rc3-git7-read_pages-fix/mm/readahead.c
@@ -182,14 +182,11 @@ static int read_pages(struct address_spa
list_del(&page->lru);
if (!add_to_page_cache(page, mapping,
page->index, GFP_KERNEL)) {
- ret = mapping->a_ops->readpage(filp, page);
- if (ret != AOP_TRUNCATED_PAGE) {
- if (!pagevec_add(&lru_pvec, page))
- __pagevec_lru_add(&lru_pvec);
- continue;
- } /* else fall through to release */
- }
- page_cache_release(page);
+ mapping->a_ops->readpage(filp, page);
+ if (!pagevec_add(&lru_pvec, page))
+ __pagevec_lru_add(&lru_pvec);
+ } else
+ page_cache_release(page);
}
pagevec_lru_add(&lru_pvec);
ret = 0;
-
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