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Sun, 18 Oct 2026 22:55:31 -0700 (PDT) Received: from google.com ([2a00:79e0:2031:6:7b3d:f4ff:823:5963]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ac94627250sm19129769a91.8.2026.10.18.22.55.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 18 Oct 2026 22:55:30 -0700 (PDT) Date: Mon, 19 Oct 2026 14:55:27 +0900 From: Sergey Senozhatsky To: Bo Zhang Cc: senozhatsky@chromium.org, akpm@linux-foundation.org, baohua@kernel.org, bgeffon@google.com, minchan@kernel.org, richardycc@google.com, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v3 10/11] zram: use rw_semaphore for decompression streams Message-ID: References: <20261016134847.1620103-1-zhangbo0325@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261016134847.1620103-1-zhangbo0325@gmail.com> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 425EE4000C X-Stat-Signature: mpuw4wrdhskim6dd1bf5ujupzf8rk87u X-Rspam-User: X-HE-Tag: 1792389332-527243 X-HE-Meta: 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 YXRu+ztg 0Ynw/XsoInUXqgaaShOvji/pktmEQ0i8t0O23P/IHuoSj8GAQnWp8lGe6AREuKOix9vZODO6Lk92wezN43HMzAyYtA/pwtnV2ExqSxy7BwU/XWbaMBA3dy8Sw1ITnWy3effVrInysbRW0kEO8029A1R6voZ3sNg8nnJ+yVBdkwz8JdqhWNmLufaRnN1+tkM2nFsxgXLhHXzvvV5rJtxuvzBRmn6s49nU34d8QE4cmORFP4OFnLDqGa8Xc1Dx6MxunxJAg/v/vK2j99ZOzURWHmfet0hiNjcfCjDMK3gcNjBE8Wmh2TGjAIbOApBH15wtUGBJsjp94hKSQgquawiyobb3B6m6w4dPqUT4Hza7K4EtN0Dn5veRAFc0HmrQXUEEvr75uXO3j02zVJgI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On (26/10/16 21:48), Bo Zhang wrote: > On Fri, 16 Oct 2026 17:54:25 +0900 Sergey Senozhatsky wrote: > > A quick and dirty patch, as usual, just to play around with. This > > attempts to improve the reader side, because the reader is side > > much more sensitive. Tested only with zstd. > > I applied the cross-CPU borrowing patch on-device and re-ran the same > zstd Android A/B, so it can be compared against the preempt-disable > numbers I posted earlier. Focusing on the read (exclusive decompression) > side, which is what this patch targets: > > 9+10+kmalloc preempt-disable cross-CPU borrow > dexcl_contended 15,919 54 1,447 > dexcl_wait_ns_total 109.6 s 0.68 s 3.66 s > dexcl_wait_ns_max 145 ms 34.6 ms 26.6 ms > dexcl_avg_wait 6.88 ms 12.6 ms 2.53 ms > dexcl_acquire 2.21M 2.75M 2.94M > > Borrowing clearly works: dexcl contention drops 15,919 -> 1,447 (-91%), > and the residual 1,447 are the genuinely all-CPUs-busy cases that fall > through to wait_event(). More importantly for us, the worst case and the > average are the best of the three - max 145ms -> 26.6ms (-82%), avg down > to 2.53ms. Thank you Bo! I included your numbers into the commit message.