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Wed, 18 Mar 2026 03:31:55 -0700 (PDT) Received: from google.com ([2a00:79e0:2031:6:2eae:ed87:1d:8a5]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b06e632418sm28236915ad.81.2026.03.18.03.31.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Mar 2026 03:31:54 -0700 (PDT) Date: Wed, 18 Mar 2026 19:31:50 +0900 From: Sergey Senozhatsky To: Hui Zhu Cc: Minchan Kim , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, teawater , Sergey Senozhatsky Subject: Re: [PATCH] zsmalloc: return -EAGAIN for zspage migration lock contention Message-ID: References: <20260318073114.34858-1-hui.zhu@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On (26/03/18 19:21), Sergey Senozhatsky wrote: > On (26/03/18 15:31), Hui Zhu wrote: > > movable_operations::migrate_page() should return -EAGAIN for temporary > > migration failures so the migration core can retry. Other negative > > errors are treated as permanent failures. > > > > zs_page_migrate() currently returns -EINVAL when zspage_write_trylock() > > fails. That path reflects transient lock contention, not invalid input. > > Returning -EINVAL misclassifies the failure and can reduce migration > > success under contention. > > The zspage's reader-lock owner can be preempted for unknown duration, > so I don't know if returning -EAGAIN is safe. On one hand, migration > attempts are limited by NR_MAX_MIGRATE_PAGES_RETRY, on the other hand, > those attempts are performed basically immediately (?), I'm not sure > if we have good chances for preempted reader-lock owner to get scheduled > and release the lock in time. .. or reader-lock owner can simply perform decompression with a very slow algorithm (e.g. deflate) which can taks significantly more time than NR_MAX_MIGRATE_PAGES_RETRY migration atteempts. So I agree that -EINVAL is not the best error code to return here. Not sure if -EAGAIN is the best one either. Technically, -EBUSY can be a candidate (this is not exactly what migration code expects and -EBUSY is not any better than -EINVAL as it's still going to be a terminal error).