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From: Yosry Ahmed To: Sergey Senozhatsky Cc: Kairui Song , Andrew Morton , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv4 02/17] zram: do not use per-CPU compression streams Message-ID: References: <20250131090658.3386285-1-senozhatsky@chromium.org> <20250131090658.3386285-3-senozhatsky@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Stat-Signature: ky47y1mb98qzbctediw6kbqtaxb1ixi5 X-Rspamd-Queue-Id: 69BBE40004 X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1738616428-523914 X-HE-Meta: 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 QxldFK6y 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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, Feb 03, 2025 at 12:49:42PM +0900, Sergey Senozhatsky wrote: > On (25/02/01 17:21), Kairui Song wrote: > > This seems will cause a huge regression of performance on multi core > > systems, this is especially significant as the number of concurrent > > tasks increases: > > > > Test build linux kernel using ZRAM as SWAP (1G memcg): > > > > Before: > > + /usr/bin/time make -s -j48 > > 2495.77user 2604.77system 2:12.95elapsed 3836%CPU (0avgtext+0avgdata > > 863304maxresident)k > > > > After: > > + /usr/bin/time make -s -j48 > > 2403.60user 6676.09system 3:38.22elapsed 4160%CPU (0avgtext+0avgdata > > 863276maxresident)k > > How many CPUs do you have? I assume, preemption gets into way which is > sort of expected, to be honest... Using per-CPU compression streams > disables preemption and uses CPU exclusively at a price of other tasks > not being able to run. I do tend to think that I made a mistake by > switching zram to per-CPU compression streams. FWIW, I am not familiar at all with the zram code but zswap uses per-CPU acomp contexts with a mutex instead of a spinlock. So the task uses the context of the CPU that it started on, but it can be preempted or migrated and end up running on a different CPU. This means that contention is still possible, but probably much lower than having a shared pool of contexts that all CPUs compete on. Again, this could be irrelevant as I am not very familiar with the zram code, just thought this may be useful.