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Wed, 7 Jan 2026 15:28:04 +0800 (CST) X-Sender: zhangdongdong925@sina.com X-Auth-ID: zhangdongdong925@sina.com X-SMAIL-MID: 8978036291840 X-SMAIL-UIID: 5D5FCF9AA3104E0E9780317D09358A48-20260107-152804-1 Message-ID: <2663a3d3-2d52-4269-970a-892d71c966bb@sina.com> Date: Wed, 7 Jan 2026 15:28:03 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv2 1/7] zram: introduce compressed data writeback To: Sergey Senozhatsky Cc: 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 References: <20251201094754.4149975-1-senozhatsky@chromium.org> <20251201094754.4149975-2-senozhatsky@chromium.org> <40e38fa7-725b-407a-917a-59c5a76dedcb@sina.com> <7bnmkuodymm33yclp6e5oir2sqnqmpwlsb5qlxqyawszb5bvlu@l63wu3ckqihc> Content-Language: en-US From: zhangdongdong In-Reply-To: <7bnmkuodymm33yclp6e5oir2sqnqmpwlsb5qlxqyawszb5bvlu@l63wu3ckqihc> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 528DB20003 X-Stat-Signature: ah49fngm1hifix96bm9rr6azq36mykpo X-Rspam-User: X-HE-Tag: 1767770888-83134 X-HE-Meta: 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 YhrG1T8Y urNJ6SOqVY1X4Qeup4LWc4xtHHc+BNLkCac2++6u/QchGo14PRA0pFrPzA5XhFxBV35QtkfLsfEuFh+/JYbkuQTldQzqz+tbMnB1/S8nUkXZIXKq5TO3K8EgEijICUOTqq2CsH2jhXKB/UFHHrYGK23v3n7MbFV63l2s8PA9mD4BN023ARjbFumrKghP2jRiEYrEwiTNu3GwhH0Gmg7LP/DV1v8Bd5mLDam0PLNdbvdEM3zmmuk6pC08IDExVGofXtcjdPCZsF8f7Ph1Ov0frE4RnVeIxcoC8EPCQbgzZc8yqS/ha31dOixi87Ni7vvME10olIOa0TcJw7dIpYypOxGec4kF6z5NV/5yI 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 1/7/26 12:28, Sergey Senozhatsky wrote: > On (26/01/07 11:50), zhangdongdong wrote: >> Hi Sergey, >> >> Thanks for the work on decompression-on-demand. >> >> One concern I’d like to raise is the use of a workqueue for readback >> decompression. In our measurements, deferring decompression to a worker >> introduces non-trivial scheduling overhead, and under memory pressure >> the added latency can be noticeable (tens of milliseconds in some cases). > > The problem is those bio completions happen in atomic context, and zram > requires both compression and decompression to be non-atomic. And we > can't do sync read on the zram side, because those bio-s are chained. > So the current plan is to look how system hi-prio per-cpu workqueue > will handle this. > > Did you try high priority workqueue? > Hi,Sergey Yes, we have tried high priority workqueues. In fact, our current implementation already uses a dedicated workqueue created with WQ_HIGHPRI and marked as UNBOUND, which handles the read/decompression path for swap-in. Below is a simplified snippet of the queue we are currently using: zgroup_read_wq = alloc_workqueue("zgroup_read", WQ_HIGHPRI | WQ_UNBOUND, 0); static int zgroup_submit_zio_async(struct zgroup_io *zio, struct zram_group *zgroup) { struct zgroup_req req = { .zio = zio, }; if (!zgroup_io_step_chg(zio, ZIO_STARTED, ZIO_INFLIGHT)) { wait_for_completion(&zio->wait); if (zio->status) zgroup_put_io(zio); return zio->status; } INIT_WORK_ONSTACK(&req.work, zgroup_submit_zio_work); queue_work(zgroup_read_wq, &req.work); flush_work(&req.work); destroy_work_on_stack(&req.work); return req.status ?: zgroup_decrypt_pages(zio); } Thanks, dongdong