From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id C5E2AC021B3 for ; Fri, 21 Feb 2025 19:52:37 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3D0896B0092; Fri, 21 Feb 2025 14:52:37 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 380136B0096; Fri, 21 Feb 2025 14:52:37 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 26ECB6B009A; Fri, 21 Feb 2025 14:52:37 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 0A3DD6B0092 for ; Fri, 21 Feb 2025 14:52:37 -0500 (EST) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 5C6531A0315 for ; Fri, 21 Feb 2025 19:52:36 +0000 (UTC) X-FDA: 83144999112.27.6284CA7 Received: from out-176.mta1.migadu.com (out-176.mta1.migadu.com [95.215.58.176]) by imf08.hostedemail.com (Postfix) with ESMTP id A4CFD160002 for ; Fri, 21 Feb 2025 19:52:34 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=Dkb0pvA1; spf=pass (imf08.hostedemail.com: domain of yosry.ahmed@linux.dev designates 95.215.58.176 as permitted sender) smtp.mailfrom=yosry.ahmed@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1740167554; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=S957pXycpJ39KxIXEb5eELZXdE7hG6Zr8xuEPgZ7kJE=; b=tQ47pbH/O4OOL6GSYektkJn/WoF0j5jX9bvK7os0ii5kG0Wq0QkoBBMW1Gu+VwhXuDjGmI NmJiM0HO2bjpwPoxBQGdf7k1MEkn7zs4aIXdGvj9U11pGwrHPjLdRFWqDIlZZ9eibus1Lp VrVB8IZZ0iZxOYjSijUMim8TU/k5bFU= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=Dkb0pvA1; spf=pass (imf08.hostedemail.com: domain of yosry.ahmed@linux.dev designates 95.215.58.176 as permitted sender) smtp.mailfrom=yosry.ahmed@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1740167554; a=rsa-sha256; cv=none; b=CkHRrUbhKoe2M+fhz6whAlUwxKlJZA1H4+tsuxiaF2ryQc4hWH85JzZLx7sqXKjW2bzhky 8pGi7zSJLhLEt+62Mu5TzNEJzUmSMkjMycC7Ag6kDjBafrWyhh89HOtsXQu5j5jLoiGQhn g6hT+LA4Oqai+d0GABSFs3ts0UkBc48= Date: Fri, 21 Feb 2025 19:52:28 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1740167553; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=S957pXycpJ39KxIXEb5eELZXdE7hG6Zr8xuEPgZ7kJE=; b=Dkb0pvA1HYJEtGlUuiyHswTgEnm84xZybKjzq6GPezBsnLtfYeW6fWJeixOlXx7h09FUIu xxbu9B2T+J3vLHGxkaYMcFK7gV7KsQ9VGHJUqtDcz141sckJ83CX9ZqKlhrHPnNH/Zmd5E KkaPNOsRNstRwBxhcpiw+lGqWoeEMrY= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yosry Ahmed To: Sergey Senozhatsky Cc: Andrew Morton , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 11/17] zsmalloc: make zspage lock preemptible Message-ID: References: <20250221093832.1949691-1-senozhatsky@chromium.org> <20250221093832.1949691-12-senozhatsky@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250221093832.1949691-12-senozhatsky@chromium.org> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: A4CFD160002 X-Stat-Signature: 53u7o7xzmqrmt5iyr3izoieiau67oixg X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1740167554-655357 X-HE-Meta: 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 cSEdzqYS RQCVA3mWNpQrSWwUBybP4yMKo9S7Oy4SQHvQc6LSmPF/csAx/XiAYMvdWJvpAp4RIn7vt/NYSTRlpMFzt+q39U60kxjg7ZXkG628KCnFjv0VEVVRAyXitdi+HrvxMzxbDuJXb40bLO19BcevGnBBfHUG0g5zU/oz/6PA20/023csuVe8cr9UwyM3YouTskI6rqLklxHlOMDjs/L7vzHzK7JooSk/1WIi09F06UZT6ivz33CeKpNtCdWk6lLWVLuiI54Du 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 Fri, Feb 21, 2025 at 06:38:04PM +0900, Sergey Senozhatsky wrote: > In order to implement preemptible object mapping we need a zspage lock > that satisfies several preconditions: > - it should be reader-write type of a lock > - it should be possible to hold it from any context, but also being > preemptible if the context allows it > - we never sleep while acquiring but can sleep while holding in read > mode > > An rwsemaphore doesn't suffice, due to atomicity requirements, rwlock > doesn't satisfy due to reader-preemptability requirement. It's also > worth to mention, that per-zspage rwsem is a little too memory heavy > (we can easily have double digits megabytes used only on rwsemaphores). > > Switch over from rwlock_t to a atomic_t-based implementation of a > reader-writer semaphore that satisfies all of the preconditions. > > The spin-lock based zspage_lock is suggested by Hillf Danton. > > Suggested-by: Hillf Danton > Signed-off-by: Sergey Senozhatsky FWIW the code looks correct to me, but I don't trust my locking knowledge enough to give a Reviewed-by :)