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Date: Thu, 6 Jun 2024 14:43:34 +0900
From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
	Yosry Ahmed <yosryahmed@google.com>,
	Erhard Furtner <erhard_f@mailbox.org>, Yu Zhao <yuzhao@google.com>,
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	linuxppc-dev@lists.ozlabs.org, Johannes Weiner <hannes@cmpxchg.org>,
	Nhat Pham <nphamcs@gmail.com>, Minchan Kim <minchan@kernel.org>,
	"Vlastimil Babka (SUSE)" <vbabka@kernel.org>
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On (24/06/06 12:46), Chengming Zhou wrote:
> >> Agree, I think we should try to improve locking scalability of zsmalloc.
> >> I have some thoughts to share, no code or test data yet:
> >>
> >> 1. First, we can change the pool global lock to per-class lock, which
> >>    is more fine-grained.
> > 
> > Commit c0547d0b6a4b6 "zsmalloc: consolidate zs_pool's migrate_lock
> > and size_class's locks" [1] claimed no significant difference
> > between class->lock and pool->lock.
> 
> Ok, I haven't looked into the history much, that seems preparation of trying
> to introduce reclaim in the zsmalloc? Not sure. But now with the reclaim code
> in zsmalloc has gone, should we change back to the per-class lock? Which is

Well, the point that commit made was that Nhat (and Johannes?) were
unable to detect any impact of pool->lock on a variety of cases.  So
we went on with code simplification.

> obviously more fine-grained than the pool lock. Actually, I have just done it,
> will test to get some data later.

Thanks, we'll need data on this.  I'm happy to take the patch, but
jumping back and forth between class->lock and pool->lock merely
"for obvious reasons" is not what I'm extremely excited about.