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From: Shakeel Butt To: Yosry Ahmed Cc: Jesper Dangaard Brouer , tj@kernel.org, cgroups@vger.kernel.org, hannes@cmpxchg.org, lizefan.x@bytedance.com, longman@redhat.com, kernel-team@cloudflare.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2] cgroup/rstat: Avoid thundering herd problem by kswapd across NUMA nodes Message-ID: References: <171923011608.1500238.3591002573732683639.stgit@firesoul> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Stat-Signature: c36bs3bskxdy1y4pp95onx6w3eoozbuo X-Rspamd-Queue-Id: A378EA0012 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1719275094-509561 X-HE-Meta: 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 szj+6Y3e 5T6cuFJoWhxi8X2jHpRppGWVHhkj6CccwRLKMTUrlvH9w0DK8Pb6KxzgntTyNHVnVOYnm1FH7FgDc3miksmagVsGOOJ4v54CwYRed69jtLfYas27bUMmc3RaLWf1REhzhMeCegncGjHfm8A9ci/7VzpQlrw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.031861, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jun 24, 2024 at 03:21:22PM GMT, Yosry Ahmed wrote: > On Mon, Jun 24, 2024 at 3:17 PM Shakeel Butt wrote: > > > > On Mon, Jun 24, 2024 at 02:43:02PM GMT, Yosry Ahmed wrote: > > [...] > > > > > > > > > There is also > > > > > a heuristic in zswap that may writeback more (or less) pages that it > > > > > should to the swap device if the stats are significantly stale. > > > > > > > > > > > > > Is this the ratio of MEMCG_ZSWAP_B and MEMCG_ZSWAPPED in > > > > zswap_shrinker_count()? There is already a target memcg flush in that > > > > function and I don't expect root memcg flush from there. > > > > > > I was thinking of the generic approach I suggested, where we can avoid > > > contending on the lock if the cgroup is a descendant of the cgroup > > > being flushed, regardless of whether or not it's the root memcg. I > > > think this would be more beneficial than just focusing on root > > > flushes. > > > > Yes I agree with this but what about skipping the flush in this case? > > Are you ok with that? > > Sorry if I am confused, but IIUC this patch affects all root flushes, > even for userspace reads, right? In this case I think it's not okay to > skip the flush without waiting for the ongoing flush. So, we differentiate between userspace and in-kernel users. For userspace, we should not skip flush and for in-kernel users, we can skip if flushing memcg is the ancestor of the given memcg. Is that what you are saying?