From: "shidao.ytt" <shidao....@alibaba-inc.com>
in commit 441c228f817f7 ("mm: fadvise: document the
fadvise(FADV_DONTNEED) behaviour for partial pages") Mel Gorman
explained why partial pages should be preserved instead of discarded
when using fadvise(FADV_DONTNEED), however the actual codes to calcuate
end_index was unexpectedly wrong, the code behavior didn't match to the
statement in comments; Luckily in another commit 18aba41cbf
("mm/fadvise.c: do not discard partial pages with POSIX_FADV_DONTNEED")
Oleg Drokin fixed this behavior
Here I come up with a new idea that actually we can still discard the
last parital page iff the page-unaligned endbyte is also the end of
file, since no one else will use the rest of the page and it should be
safe enough to discard.
Signed-off-by: shidao.ytt <shidao....@alibaba-inc.com>
Signed-off-by: Caspar Zhang <jinli....@alibaba-inc.com>
---
mm/fadvise.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/fadvise.c b/mm/fadvise.c
index ec70d6e..f74b21e 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -127,7 +127,8 @@
*/
start_index = (offset+(PAGE_SIZE-1)) >> PAGE_SHIFT;
end_index = (endbyte >> PAGE_SHIFT);
- if ((endbyte & ~PAGE_MASK) != ~PAGE_MASK) {
+ if ((endbyte & ~PAGE_MASK) != ~PAGE_MASK &&
+ endbyte != inode->i_size - 1) {
/* First page is tricky as 0 - 1 = -1, but pgoff_t
* is unsigned, so the end_index >= start_index
* check below would be true and we'll discard the whole
--
1.8.3.1
