The patch titled
Subject: mm/filemap.c: don't bother dropping mmap_sem for zero size readahead
has been added to the -mm tree. Its filename is
mm-dont-bother-dropping-mmap_sem-for-zero-size-readahead.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-dont-bother-dropping-mmap_sem-for-zero-size-readahead.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-dont-bother-dropping-mmap_sem-for-zero-size-readahead.patch
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------------------------------------------------------
From: Jan Kara <jack@xxxxxxx>
Subject: mm/filemap.c: don't bother dropping mmap_sem for zero size readahead
When handling a page fault, we drop mmap_sem to start async readahead so
that we don't block on IO submission with mmap_sem held. However there's
no point to drop mmap_sem in case readahead is disabled. Handle that case
to avoid pointless dropping of mmap_sem and retrying the fault. This was
actually reported to block mlockall(MCL_CURRENT) indefinitely.
Link: http://lkml.kernel.org/r/20200212101356.30759-1-jack@xxxxxxx
Fixes: 6b4c9f446981 ("filemap: drop the mmap_sem for all blocking operations")
Signed-off-by: Jan Kara <jack@xxxxxxx>
Reported-by: Minchan Kim <minchan@xxxxxxxxxx>
Reported-by: Robert Stupp <snazy@xxxxxx>
Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Reviewed-by: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/filemap.c~mm-dont-bother-dropping-mmap_sem-for-zero-size-readahead
+++ a/mm/filemap.c
@@ -2419,7 +2419,7 @@ static struct file *do_async_mmap_readah
pgoff_t offset = vmf->pgoff;
/* If we don't want any read-ahead, don't bother */
- if (vmf->vma->vm_flags & VM_RAND_READ)
+ if (vmf->vma->vm_flags & VM_RAND_READ || !ra->ra_pages)
return fpin;
mmap_miss = READ_ONCE(ra->mmap_miss);
if (mmap_miss)
_
Patches currently in -mm which might be from jack@xxxxxxx are
mm-dont-bother-dropping-mmap_sem-for-zero-size-readahead.patch
