+ mmap-locking-api-add-mmap_lock_is_contended.patch added to -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mmap locking API: add mmap_lock_is_contended()
has been added to the -mm tree.  Its filename is
     mmap-locking-api-add-mmap_lock_is_contended.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mmap-locking-api-add-mmap_lock_is_contended.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mmap-locking-api-add-mmap_lock_is_contended.patch

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------------------------------------------------------
From: Chinwen Chang <chinwen.chang@mediatek.com>
Subject: mmap locking API: add mmap_lock_is_contended()

Patch series "Try to release mmap_lock temporarily in smaps_rollup", v4.

Recently, we have observed some janky issues caused by unpleasantly long
contention on mmap_lock which is held by smaps_rollup when probing large
processes.  To address the problem, we let smaps_rollup detect if anyone
wants to acquire mmap_lock for write attempts.  If yes, just release the
lock temporarily to ease the contention.

smaps_rollup is a procfs interface which allows users to summarize the
process's memory usage without the overhead of seq_* calls.  Android uses
it to sample the memory usage of various processes to balance its memory
pool sizes.  If no one wants to take the lock for write requests,
smaps_rollup with this patch will behave like the original one.

Although there are on-going mmap_lock optimizations like range-based
locks, the lock applied to smaps_rollup would be the coarse one, which is
hard to avoid the occurrence of aforementioned issues.  So the detection
and temporary release for write attempts on mmap_lock in smaps_rollup is
still necessary.


This patch (of 3):

Add new API to query if someone wants to acquire mmap_lock for write
attempts.

Using this instead of rwsem_is_contended makes it more tolerant of future
changes to the lock type.

Link: http://lkml.kernel.org/r/1597715898-3854-1-git-send-email-chinwen.chang@mediatek.com
Link: http://lkml.kernel.org/r/1597715898-3854-2-git-send-email-chinwen.chang@mediatek.com
Signed-off-by: Chinwen Chang <chinwen.chang@mediatek.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Acked-by: Michel Lespinasse <walken@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Daniel Kiss <daniel.kiss@arm.com>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jimmy Assarsson <jimmyassarsson@gmail.com>
Cc: Laurent Dufour <ldufour@linux.ibm.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mmap_lock.h |    5 +++++
 1 file changed, 5 insertions(+)

--- a/include/linux/mmap_lock.h~mmap-locking-api-add-mmap_lock_is_contended
+++ a/include/linux/mmap_lock.h
@@ -87,4 +87,9 @@ static inline void mmap_assert_write_loc
 	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
 }
 
+static inline int mmap_lock_is_contended(struct mm_struct *mm)
+{
+	return rwsem_is_contended(&mm->mmap_lock);
+}
+
 #endif /* _LINUX_MMAP_LOCK_H */
_

Patches currently in -mm which might be from chinwen.chang@mediatek.com are

mmap-locking-api-add-mmap_lock_is_contended.patch
mm-smaps-extend-smap_gather_stats-to-support-specified-beginning.patch
mm-proc-smaps_rollup-do-not-stall-write-attempts-on-mmap_lock.patch