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Wed, 05 Aug 2026 01:46:07 -0700 (PDT) Received: from google.com ([2a00:79e0:2031:6:8002:2a47:a704:5a58]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cbe708be5bdsm1024528a12.15.2026.08.05.01.46.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Aug 2026 01:46:07 -0700 (PDT) Date: Wed, 5 Aug 2026 17:46:02 +0900 From: Sergey Senozhatsky To: Barry Song Cc: Sergey Senozhatsky , akpm@linux-foundation.org, bigeasy@linutronix.de, hdanton@sina.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, minchan@kernel.org, ryncsn@gmail.com, yosry.ahmed@linux.dev, surenb@google.com, Dongdong Zhang , Suleiman Souhlal Subject: Re: [RFC PATCH] zram: avoid preemption with CPU-based compression backends Message-ID: References: <20260805005545.66112-1-baohua@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: EDF99140005 X-Stat-Signature: romfhxjgm9beq3gti4j6swxaemexdjdr X-HE-Tag: 1785919568-809479 X-HE-Meta: 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 lswNbcEY yTt1QRFyO8TPZpl2xImcQallOe6FE4JsM8Ly0QYDIgODoh5vr7AsJh6WLwBtCNIi+SGjiemtrGX+F9LIreL/nDoZ/0Yl4O5yYplitm7Asqj2Qgn0nXfaMzusV3bOW3RaU3Ak/zvufhFR53ILGLk6Nn89qK77jCZps/H9owLR0fZYniKTm17hz+Wlp+oxp0skM+KOoVQ0MpHQ5slb6w5JVjePT5KhqAT4ZjUC6C8/N0YLmt6uVJvX4/Ra8ENkbyiwrDMNwzfQBWaxJW8Hs6rSVbbuGa5rCIS45iUnwcPFS23rW6euklHZliSRT+PZsoQPg5g0SAQJ9O4GNuMn0qXb52hdcgTOPTDzl4SKcNno4lLlG+pQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On (26/08/05 15:50), Barry Song wrote: > > > talked with our engineers reporting the issue. i believe it is all > > > about priority inversion. > > > proxy execution wont resolve it as we have a sleepable zs-malloc > > > within the mutex. > > > i believe i need v2 to release the mutex before doing the 2nd stage > > > zs_malloc with > > > direct reclaim. > > > > Well, we cannot just drop the stream mutex and do sleepable zsmalloc > > allocation, because this will invalidate compression buffer. So we > > then will need to do re-compression. Something that I was really > > happy to drop [1]. > [..] > BTW, I wonder if compression and decompression could use separate > mutexes. That way, a sleepable zs_malloc() in the compression path > would not block decompression, which is the more latency-sensitive > operation. This sounds interesting. I think all of the S/W backends that we use have stateless decompression, so we probably can just split per-CPU stream mutex for R and W paths w/o the need for any additional scratch buffers. Wanna give it a try? Back to preemption: Is there maybe a common hot preemption point where stream mutex owners get scheduled out? E.g. inside zs_malloc()?