lkml.org 
[lkml]   [2015]   [Feb]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] fs: avoid locking sb_lock in grab_super_passive()
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().


\
 
 \ /
  Last update: 2015-02-21 04:01    [W:0.095 / U:0.704 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site