From: Chinwen Chang Date: Tue, 13 Oct 2020 23:53:39 +0000 (-0700) Subject: mmap locking API: add mmap_lock_is_contended() X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=07e5bfe651f8595ca6a777d989016aa8d8217924;p=uclinux-h8%2Flinux.git 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. Signed-off-by: Chinwen Chang Signed-off-by: Andrew Morton Reviewed-by: Steven Price Acked-by: Michel Lespinasse Cc: Alexey Dobriyan Cc: Daniel Jordan Cc: Daniel Kiss Cc: Davidlohr Bueso Cc: Huang Ying Cc: Jason Gunthorpe Cc: Jimmy Assarsson Cc: Laurent Dufour Cc: "Matthew Wilcox (Oracle)" Cc: Matthias Brugger Cc: Song Liu Cc: Vlastimil Babka 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: Linus Torvalds --- diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h index 0707671851a8..18e7eae9b5ba 100644 --- a/include/linux/mmap_lock.h +++ b/include/linux/mmap_lock.h @@ -87,4 +87,9 @@ static inline void mmap_assert_write_locked(struct mm_struct *mm) 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 */