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Mon, 10 Mar 2025 21:58:33 -0700 (PDT) Date: Tue, 11 Mar 2025 13:58:24 +0900 From: Sergey Senozhatsky To: Qun-Wei Lin Cc: Nhat Pham , Barry Song <21cnbao@gmail.com>, Jens Axboe , Minchan Kim , Sergey Senozhatsky , Vishal Verma , Dan Williams , Dave Jiang , Ira Weiny , Andrew Morton , Matthias Brugger , AngeloGioacchino Del Regno , Chris Li , Ryan Roberts , "Huang, Ying" , Kairui Song , Dan Schatzberg , Al Viro , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, nvdimm@lists.linux.dev, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, Casper Li , Chinwen Chang , Andrew Yang , James Hsu Subject: Re: [PATCH 0/2] Improve Zram by separating compression context from kswapd Message-ID: References: <20250307120141.1566673-1-qun-wei.lin@mediatek.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: DCA7F80006 X-Stat-Signature: tnzi6jeteeccc75jxzfaqoge6hsmcmfp X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1741669114-892975 X-HE-Meta: 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 7EZHP7Fh 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000010, 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 (25/03/08 18:41), Barry Song wrote: > On Sat, Mar 8, 2025 at 12:03 PM Nhat Pham wrote: > > > > On Fri, Mar 7, 2025 at 4:02 AM Qun-Wei Lin wrote: > > > > > > This patch series introduces a new mechanism called kcompressd to > > > improve the efficiency of memory reclaiming in the operating system. The > > > main goal is to separate the tasks of page scanning and page compression > > > into distinct processes or threads, thereby reducing the load on the > > > kswapd thread and enhancing overall system performance under high memory > > > pressure conditions. > > > > Please excuse my ignorance, but from your cover letter I still don't > > quite get what is the problem here? And how would decouple compression > > and scanning help? > > My understanding is as follows: > > When kswapd attempts to reclaim M anonymous folios and N file folios, > the process involves the following steps: > > * t1: Time to scan and unmap anonymous folios > * t2: Time to compress anonymous folios > * t3: Time to reclaim file folios > > Currently, these steps are executed sequentially, meaning the total time > required to reclaim M + N folios is t1 + t2 + t3. > > However, Qun-Wei's patch enables t1 + t3 and t2 to run in parallel, > reducing the total time to max(t1 + t3, t2). This likely improves the > reclamation speed, potentially reducing allocation stalls. If compression kthread-s can run (have CPUs to be scheduled on). This looks a bit like a bottleneck. Is there anything that guarantees forward progress? Also, if compression kthreads constantly preempt kswapd, then it might not be worth it to have compression kthreads, I assume? If we have a pagefault and need to map a page that is still in the compression queue (not compressed and stored in zram yet, e.g. dut to scheduling latency + slow compression algorithm) then what happens?