The patch titled
Subject: mm: fadvise: avoid fadvise for fs without backing device
has been added to the -mm tree. Its filename is
mm-fadvise-avoid-fadvise-for-fs-without-backing-device.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-fadvise-avoid-fadvise-for-fs-without-backing-device.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-fadvise-avoid-fadvise-for-fs-without-backing-device.patch
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From: Shakeel Butt <shakeelb@xxxxxxxxxx>
Subject: mm: fadvise: avoid fadvise for fs without backing device
The fadvise() manpage is silent on fadvise()'s effect on memory-based
filesystems (shmem, hugetlbfs & ramfs) and pseudo file systems (procfs,
sysfs, kernfs). The current implementaion of fadvise is mostly a noop for
such filesystems except for FADV_DONTNEED which will trigger expensive
remote LRU cache draining. This patch makes the noop of fadvise() on such
file systems very explicit.
However this change has two side effects for ramfs and one for tmpfs.
First fadvise(FADV_DONTNEED) can remove the unmapped clean zero'ed pages
of ramfs (allocated through read, readahead & read fault) and tmpfs
(allocated through read fault). Also fadvise(FADV_WILLNEED) on create
such clean zero'ed pages for ramfs. This change removes these two
interfaces.
One of our generic librarise does fadvise(FADV_DONTNEED). Recently we
observed high latency in fadvise() and noticed that the users have started
using tmpfs files and the latency was due to expensive remote LRU cache
draining. For normal tmpfs files (have data written on them),
fadvise(FADV_DONTNEED) will always trigger the unneeded remote cache
draining.
Link: http://lkml.kernel.org/r/20170818011023.181465-1-shakeelb@xxxxxxxxxx
Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/fadvise.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff -puN mm/fadvise.c~mm-fadvise-avoid-fadvise-for-fs-without-backing-device mm/fadvise.c
--- a/mm/fadvise.c~mm-fadvise-avoid-fadvise-for-fs-without-backing-device
+++ a/mm/fadvise.c
@@ -52,7 +52,9 @@ SYSCALL_DEFINE4(fadvise64_64, int, fd, l
goto out;
}
- if (IS_DAX(inode)) {
+ bdi = inode_to_bdi(mapping->host);
+
+ if (IS_DAX(inode) || (bdi == &noop_backing_dev_info)) {
switch (advice) {
case POSIX_FADV_NORMAL:
case POSIX_FADV_RANDOM:
@@ -75,8 +77,6 @@ SYSCALL_DEFINE4(fadvise64_64, int, fd, l
else
endbyte--; /* inclusive */
- bdi = inode_to_bdi(mapping->host);
-
switch (advice) {
case POSIX_FADV_NORMAL:
f.file->f_ra.ra_pages = bdi->ra_pages;
_
Patches currently in -mm which might be from shakeelb@xxxxxxxxxx are
mm-fadvise-avoid-fadvise-for-fs-without-backing-device.patch
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