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 50376C48285 for ; Mon, 29 Jan 2024 16:28:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AF8796B007E; Mon, 29 Jan 2024 11:28:53 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id AA8886B0080; Mon, 29 Jan 2024 11:28:53 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 96FC96B0081; Mon, 29 Jan 2024 11:28:53 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 8707C6B007E for ; Mon, 29 Jan 2024 11:28:53 -0500 (EST) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 55C92A1F23 for ; Mon, 29 Jan 2024 16:28:53 +0000 (UTC) X-FDA: 81732882546.03.A9195BA Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.223.130]) by imf29.hostedemail.com (Postfix) with ESMTP id 3EAB3120026 for ; Mon, 29 Jan 2024 16:28:49 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=XUTLamqS; dkim=pass header.d=suse.com header.s=susede1 header.b=XUTLamqS; spf=pass (imf29.hostedemail.com: domain of mhocko@suse.com designates 195.135.223.130 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1706545730; a=rsa-sha256; cv=none; b=UpPrn1zThdg6StLbOv/keqjqPUO9tJHsJKIEAQuC7qBJrRXnL8Cf9RNtqKYwxlmP8WtGGe +cZAOKOyzEi51oX5LOE3G6mXMM1Dx5x6gVAAr6oAXkTlOVaFeQKLMnI86Kprmtyn7n0J8o nJaYnh5R3LesbaTdw/t7Hmk9PjFW1yg= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=XUTLamqS; dkim=pass header.d=suse.com header.s=susede1 header.b=XUTLamqS; spf=pass (imf29.hostedemail.com: domain of mhocko@suse.com designates 195.135.223.130 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1706545730; 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=xNOhVEGA1+wfkSw8lLpS1nHrin/VwWv41XiZwlbriU0=; b=v66B6sn5J1fiwLmvcbRflvs98i8V6CJ7N1ndZMDSggExt7UCoOcKTSMhk+sDO7nHVOM+Q3 bibzPRgGdft9hl1mN7UnnEG6rK3UZzpD+YCfN7zkjszoOChqxNdli4wpmXPm2kQ8xtS1F4 byej+mG9HQHhpiyP0vxM0zC7cLaCUTI= Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 50EB322113; Mon, 29 Jan 2024 16:28:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1706545728; h=from:from:reply-to: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=xNOhVEGA1+wfkSw8lLpS1nHrin/VwWv41XiZwlbriU0=; b=XUTLamqS6cd43HyhnadirfxcREIIdcSOwpPQRua7eYb0PQE6FwmmZFjot86SHgO4lr2i11 qkNTftHHazJjiCwG00CUWJ+G4hiywzyL5mq/aenxyeVDiiEOVLmcwqzU3eruhQKNUVYqMV 1SZy3nK9L/8NGIeJmwW4VTNi5A0IAjI= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1706545728; h=from:from:reply-to: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=xNOhVEGA1+wfkSw8lLpS1nHrin/VwWv41XiZwlbriU0=; b=XUTLamqS6cd43HyhnadirfxcREIIdcSOwpPQRua7eYb0PQE6FwmmZFjot86SHgO4lr2i11 qkNTftHHazJjiCwG00CUWJ+G4hiywzyL5mq/aenxyeVDiiEOVLmcwqzU3eruhQKNUVYqMV 1SZy3nK9L/8NGIeJmwW4VTNi5A0IAjI= Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 2B30012FF7; Mon, 29 Jan 2024 16:28:48 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 8lD2BkDSt2V0UwAAD6G6ig (envelope-from ); Mon, 29 Jan 2024 16:28:48 +0000 Date: Mon, 29 Jan 2024 17:28:47 +0100 From: Michal Hocko To: Lance Yang Cc: akpm@linux-foundation.org, zokeefe@google.com, david@redhat.com, songmuchun@bytedance.com, shy828301@gmail.com, peterx@redhat.com, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] mm/khugepaged: bypassing unnecessary scans with MMF_DISABLE_THP check Message-ID: References: <20240129054551.57728-1-ioworker0@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240129054551.57728-1-ioworker0@gmail.com> X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 3EAB3120026 X-Stat-Signature: dohdhwkjy4398adyi1ygedxzx7mmx45k X-Rspam-User: X-HE-Tag: 1706545729-521561 X-HE-Meta: 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 3/a0l0To 9DDvlP2i3JmjR7xGXN+YWP9/aB/iQh4Et4taNr+Mmunj8IYOQmqtGu6NoTCBWlH2PKDrfWKPdqRiHdQr0XUzvqUyF5liWTCxvgkop1QaTFYtWnKxVKy+chH5uVtLvTqM38+P/K97mqZCTzxeAuHWJs0og87i13B5VCEi5QEkgUJIuckEdOoR1xvOtqxbF5y/78x6mjVf3EJB7ylzjZe8KSUogIgdpyN8J/7hFBBLbGiG/UB8bDmRUTvJQPb082UtGy51T6TuhmXIg6OsZpB95e9Z4JvHPY2NAMtln X-Bogosity: Ham, tests=bogofilter, spamicity=0.000699, 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 Mon 29-01-24 13:45:51, Lance Yang wrote: > khugepaged scans the entire address space in the > background for each given mm, looking for > opportunities to merge sequences of basic pages > into huge pages. However, when an mm is inserted > to the mm_slots list, and the MMF_DISABLE_THP flag > is set later, this scanning process becomes > unnecessary for that mm and can be skipped to avoid > redundant operations, especially in scenarios with > a large address space. Is this a real problem? I thought that the prctl is called on the parent before fork/exec. Or are you aware of any applications which do call prctl late enough that the race would be actually observable? -- Michal Hocko SUSE Labs