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Thu, 20 Nov 2025 23:58:46 -0800 (PST) Received: from google.com ([2401:fa00:8f:203:b321:53f:aff8:76e2]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7c3ed47b388sm5171421b3a.27.2025.11.20.23.58.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Nov 2025 23:58:45 -0800 (PST) Date: Fri, 21 Nov 2025 16:58:41 +0900 From: Sergey Senozhatsky To: Yuwen Chen Cc: senozhatsky@chromium.org, akpm@linux-foundation.org, bgeffon@google.com, licayy@outlook.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, minchan@kernel.org, richardycc@google.com Subject: Re: [RFC PATCHv5 0/6] zram: introduce writeback bio batching Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 6B13C160004 X-Stat-Signature: xwk3zp6g1dpunt9t43iz5xhw6o1hpg4s X-Rspam-User: X-HE-Tag: 1763711927-251828 X-HE-Meta: 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 BYeD7QIj mtFFrbykn706IjLsiipz46LTnvRdmKTqhcXJUPzCfpIOsYwLP2XBhpiCF086DqzYxXt2wIbzQay1hvcdR1YQ3tyJOmsllv9zFCObFdnb9xLTsSelVpIqUdNL/Zbd9ZtOfbS8BhQ4YkuBs4ev1VrTyCaM7L53J21q+UCEUy5OMKVeqcLqfWq6k0fLxM61Hc+Oc6q84AJA7Qe0LL4nwAtBmoeq7sibGzDoMHGGQ8WU9/Ggc6aH8xSv4yHYfRijFBH8t9FZuUINeOLIcLcZEO22Wlf+3yRjeJtE22NdwYq+p4lzsMrdWbiixDthUkBIA6P7gqHgqH9pXkaoVNaIS5Bu+V0Cg72PXRGCOyoi0VkCz9+Z3cVM= 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 (25/11/21 15:44), Yuwen Chen wrote: > On Fri, 21 Nov 2025 16:32:27 +0900, Sergey Senozhatsky wrote: > > Is "before" blk-plug based approach and "after" this new approach? > > Sorry, I got the before and after mixed up. No problem. I wonder if the effect is more visible on larger data sets. 0.3 second sounds like a very short write. In my VM tests I couldn't get more than 2 inflight requests at a time, I guess because decompression was much slower than IO. I wonder how many inflight requests you had in your tests. > In addition, I also have some related questions to consult: > > 1. Will page fault exceptions be delayed during the writeback processing? I don't think our reads are blocked by writes. > 2. Since the loop device uses a work queue to handle requests, when > the system load is relatively high, will it have a relatively large > impact on the latency of page fault exceptions? Is there any way to solve > this problem? I think page-fault latency of a written-back page is expected to be higher, that's a trade-off that we agree on. Off the top of my head, I don't think we can do anything about it. Is loop device always used as for writeback targets?