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Mon, 12 Jan 2026 20:54:09 -0800 (PST) Received: from google.com ([2a00:79e0:2031:6:3c61:f146:e418:e233]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c59b0bf72afsm6489637a12.28.2026.01.12.20.54.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Jan 2026 20:54:08 -0800 (PST) Date: Tue, 13 Jan 2026 13:54:02 +0900 From: Sergey Senozhatsky To: zhangdongdong Cc: Sergey Senozhatsky , Jens Axboe , Andrew Morton , Richard Chang , Minchan Kim , Brian Geffon , David Stevens , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, Minchan Kim , xiongping1@xiaomi.com, huangjianan@xiaomi.com, wanghui33@xiaomi.com Subject: Re: [PATCHv2 1/7] zram: introduce compressed data writeback Message-ID: References: <20251201094754.4149975-1-senozhatsky@chromium.org> <20251201094754.4149975-2-senozhatsky@chromium.org> <40e38fa7-725b-407a-917a-59c5a76dedcb@sina.com> <7bnmkuodymm33yclp6e5oir2sqnqmpwlsb5qlxqyawszb5bvlu@l63wu3ckqihc> <2663a3d3-2d52-4269-970a-892d71c966bb@sina.com> <731f6e5b-f678-49ef-ad8e-fe6ff85d5422@sina.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <731f6e5b-f678-49ef-ad8e-fe6ff85d5422@sina.com> X-Rspam-User: X-Stat-Signature: hmoe6gi43s5habckoye4crkf9xj5hf48 X-Rspamd-Queue-Id: 7DFB71C0008 X-Rspamd-Server: rspam04 X-HE-Tag: 1768280050-346935 X-HE-Meta: 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 Ze1Quc5p ZyOUxN7YVenZEcdWzjXYp+v74Ulpjdt/vlc+ltT5/1yhzodBiBQ3/+M/ekT42UmLklkARXh1M6709dwZonRfP6vH9svJ276y054mzVR2waC7OjZOoizyNPAaK6MjY/u8jSiVFlR5GmCds+5oz69ydmV+ajyZKOXDHyc9hecyswWgxm4HqgtVMuymNNujuP8ben/Fr2om6/IpjT8dhGDznUP1PBQ3O7j0K3qoyLZjMCqCKwJnwxlV/glCyZVMc7lZcwdn93sLEqfxJZQGJeffc7vKVoOPlhnPZfOrnAG45LyOYnpBKLaQyM+/F1kf+35VrzVLMyU95drvFTtRstONJ6ZznsVHO6s0WETyvqtOD7vuP0RM= 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: Hi, On (26/01/08 18:36), zhangdongdong wrote: [..] > > I don't know if solving it on zram side alone is possible. Maybe we > > can get some help from the block layer: some sort of two-stage bio > > submission. First stage: submit chained bio-s, second stage: iterate > > over all submitted and completed bio-s and decompress the data. Again, > > just thinking out loud. > > > > Hi Sergey, > > My thinking is largely aligned with yours. I agree that relying on zram > alone is unlikely to fully solve this problem, especially without going > back to atomic read/write. > > Our current mitigation approach is to introduce a hook at the swap layer > and move decompression there. By doing so, decompression happens in a > fully sleepable context, which avoids the atomic-context constraints > you outlined. This helps us sidestep the core issue rather than trying > to force decompression back into zram completion paths. This approach is limited to swap use-cases only, while zram is a generic block device: one can mkfs on it and use it as a normal block device. So, this is not a complete solution. [..] > If I recall correctly, this issue first became noticeable after a block > layer change was merged; I can try to dig that up and share more details > later. Interesting.