From: Chinwen Chang <chinwen.chang@xxxxxxxxxxxx> 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@xxxxxxxxxxxx Link: http://lkml.kernel.org/r/1597715898-3854-2-git-send-email-chinwen.chang@xxxxxxxxxxxx Signed-off-by: Chinwen Chang <chinwen.chang@xxxxxxxxxxxx> Reviewed-by: Steven Price <steven.price@xxxxxxx> Acked-by: Michel Lespinasse <walken@xxxxxxxxxx> Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx> Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> Cc: Daniel Kiss <daniel.kiss@xxxxxxx> Cc: Davidlohr Bueso <dbueso@xxxxxxx> Cc: Huang Ying <ying.huang@xxxxxxxxx> Cc: Jason Gunthorpe <jgg@xxxxxxxx> Cc: Jimmy Assarsson <jimmyassarsson@xxxxxxxxx> Cc: Laurent Dufour <ldufour@xxxxxxxxxxxxx> Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Cc: Matthias Brugger <matthias.bgg@xxxxxxxxx> Cc: Song Liu <songliubraving@xxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- 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 */ _
