Messages in this thread | | | Date | Sat, 21 Feb 2015 02:37:55 +0000 | From | Al Viro <> | Subject | Re: [PATCH] fs: avoid locking sb_lock in grab_super_passive() |
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On Thu, Feb 19, 2015 at 08:19:35PM +0300, Konstantin Khlebnikov wrote: > I've noticed significant locking contention in memory reclaimer around > sb_lock inside grab_super_passive(). Grab_super_passive() is called from > two places: in icache/dcache shrinkers (function super_cache_scan) and > from writeback (function __writeback_inodes_wb). Both are required for > progress in memory reclaimer. > > Also this lock isn't irq-safe. And I've seen suspicious livelock under > serious memory pressure where reclaimer was called from interrupt which > have happened right in place where sb_lock is held in normal context, > so all other cpus were stuck on that lock too.
Excuse me, but this part is BS - its call is immediately preceded by if (!(sc->gfp_mask & __GFP_FS)) return SHRINK_STOP; and if we *ever* hit GFP_FS allocation from interrupt, we are really screwed. If nothing else, both prune_dcache_sb() and prune_icache_sb() can wait for all kinds of IO; you really don't want that called in an interrupt context. The same goes for writeback_sb_inodes(), while we are at it.
If you ever see that in an interrupt context, you have a very bad problem on hands.
Said that, not bothering with sb_lock (and ->s_count) in those two callers makes sense. Applied, with name changed to trylock_super().
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