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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7E1F3C43458 for ; Tue, 30 Jun 2026 06:41:20 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 648A16B00AA; Tue, 30 Jun 2026 02:41:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 620E06B00AB; Tue, 30 Jun 2026 02:41:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 535A96B00AC; Tue, 30 Jun 2026 02:41:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 2E3506B00AA for ; Tue, 30 Jun 2026 02:41:19 -0400 (EDT) Received: from smtpin17.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id A3F221C64B7 for ; Tue, 30 Jun 2026 06:41:18 +0000 (UTC) X-FDA: 84935632236.17.8EED813 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf20.hostedemail.com (Postfix) with ESMTP id DEB911C0002 for ; Tue, 30 Jun 2026 06:41:16 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=MFB6IX51; spf=pass (imf20.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1782801677; b=QXgEaywoJMtXDVDZPWZgoBqom/OECu16TXz78AaDTMD7ej0Rqsq0tkpoJw81xCivsSGYBx kjSxN3QHx/8d8wbItydm2EGsk5k9EAkAuqYHyO3Wwx481ASeL7Agt8HZ1D6HriS1UOmrx4 JThmfSbIdwvh7VIwThXrX5kNmddeyNQ= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782801677; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=nI2NQuj9axv7/9GpcIQsccJdAB4fSHkpahn0YO/2zjs=; b=gAmtTS701mK7vcn9hlh8RIYr+xIxVlWfgY9NU5Jkv9ejYob9VX9JVOPVK3C5r30+g0qPmK OwiJzYH2/VXw3wa243NekeEpoppyOnaJv43NOUKh7eODYO2gMhQeLZoj9+RrLN5VmPZRat ee/jQ40ok0ziVr7+aHOa4y27zn5C7mI= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=MFB6IX51; spf=pass (imf20.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id F364F41820; Tue, 30 Jun 2026 06:41:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1B4421F000E9; Tue, 30 Jun 2026 06:41:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782801675; bh=nI2NQuj9axv7/9GpcIQsccJdAB4fSHkpahn0YO/2zjs=; h=Date:Subject:From:To:Cc:References:In-Reply-To; b=MFB6IX51UbWeIAS409nXOBLdnR1JlNtyXp9puSvgJvGFWdSCOmehHKqu3qPIiKa11 3oe44E3mkkab2kDp47lU+FDliMetYVAXG4i9762UnIatpbgIMk2erzvstLqLlse5gW thLA67JMpu8TaRumNcbskKicY5MfP5DG95E76WU+cmN6s3y25sd6lWzec+wRFVMEZR uc23iP4xMkxGR8VIHqy7upIO+4pg6IWCdueNrIqj+ifmOLIXCTJB2BffmVWCR7jMZy 1fA1IcNPhVipd6NgCX2yRODTKOZ5b7Nl3glTypFKXOAk8d4rCxuCq8hnw+H0xARgjy 8y+UpG9sCrpwg== Message-ID: Date: Tue, 30 Jun 2026 08:41:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] mm: memory-failure: fix HWPoison flag race with non-atomic page flag ops From: "David Hildenbrand (Arm)" To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, Miaohe Lin , Naoya Horiguchi , Andrew Morton , Oscar Salvador , Andi Kleen , Hidehiro Kawai , Rik van Riel , Vlastimil Babka , Lorenzo Stoakes , "Liam R. 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: DEB911C0002 X-Stat-Signature: xkehgudmoyzd184bb7dgdnkpjp7f9met X-HE-Tag: 1782801676-844670 X-HE-Meta: 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 mMlEt9mf h0Hp/iCbJYkqYMpBBht0TaaZ+2e7UCTIyj4aMeKNcY15JeWXku4deuhXH+R2SFiS7Eet69IJyrqoTulne6yBO3j01xhULeXTNvQlL7JAojxutGs0U2UcJvWSF0G+faUIrhSnH6Sr6L6spMT321Sy5B/LSIjshekRxzZkCPLfjlFLPFqDlam8GO4fnscd5FFpYVahJTb9JwUjV9BB+kcS2DMcDciPnTRdPC842dg6HNH96TrthiEPNYddyngBeYBFTDEeR1LyxJJ8486Mt+mqX/aWaqlXclLKklwIlbgKQeKaQZlvWKLcJKqLEjIMrXjcr3zi+FhbG9eoUSltOqVGF8bDCuw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/30/26 08:30, David Hildenbrand (Arm) wrote: > On 6/29/26 23:50, Michael S. Tsirkin wrote: >> On Mon, Jun 29, 2026 at 11:22:11PM +0200, David Hildenbrand (Arm) wrote: >>> [...] >>> >>> >>> Fully agreed. I was hoping RCU was cheaper (I mean, we were once told that RCU >>> read side locking is essentially for free ... well in some configs :) ) >>> >>> The question if we could optimize it reasonably enough ... >>> >>> >>> ... for example, by doing the rcu read lock + unlock around the >>> >>> for (i = 1; i < (1 << order); i++) { >>> >>> loop on the alloc path. >> >> Is this different from what this patch is doing? > > Ah, I missed that we batch this already. We could make it include the > > page_cpupid_reset_last(page); > page->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP; > > As well, to reduce from 3 to 1 locks. > > So I guess there is potential for optimization. > > [...] > >> >>> I concluded, similar to Andi, that stop_machine() is too big of a hammer. >>> >>> I wonder if something could be built out of preempt_disable() and sync SMP >>> calls. hmm :( >> >> rcu_lock is basically same as preempt_disable if rcu is non preemptible, >> no? > > Yes. See my other mail, I learned that preempt_disable() should likely just do > for our use case. So the preemptible RCU case would not matter. > > I assume that's as good as it gets. > > 1) Use preempt_disable/preempt_enable to protect > 2) Batch as good as possible in the page allocator > > If the overhead is then still noticeable, there is not a lot we can do to handle > this cleanly I'm afraid. FWIW, there seems to be preempt_enable_no_resched() that is a bit more lightweight. I'm sure there is some downside, but it might be worth a try. -- Cheers, David