From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 477333859FF for ; Mon, 2 Mar 2026 08:00:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772438413; cv=none; b=gU+2SqNJWHFPR45vPXmThMGHdrMD56A4b+lCLn/uDNKhO4uNJSWUhTc5Ru95WDjnIrR2YMJKRRYYJ9dYzNzv+ISltykDtMNbemCsQNpS9OQSGsHvDO9Y/KqGxLe+W+Ggm5/TZ8NSzfjjpuSvb92yoZo+j3LHi5bJmcbN/tSy72s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772438413; c=relaxed/simple; bh=cmG85q4RbxGqFpEaUSYdNicB6sCiTJz7vAbf0cPsPyQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Y+KoYMkB4KMcSJ16+I7AjNAvH/VQkhAvToTXXWgamS981Y+qqeI1BA133gHUqRrm5g3tlFtdL38GIrXKUy8tKHSa3aaNP3paEcdbkZTew/pCOJyCBZSTOHy4y/UlyrUNJkkrljEjgJm+2IT27O9iJmkhAAYzKmnzxRr9s0+xCWQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=t5NMGNEx; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="t5NMGNEx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E225DC19423; Mon, 2 Mar 2026 08:00:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772438412; bh=cmG85q4RbxGqFpEaUSYdNicB6sCiTJz7vAbf0cPsPyQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=t5NMGNExCtSd54JUoQ3qnl7voa2g+twGcVcnFZU/PS9I2YOA4Id/TaHnMAKC+iN5M wPhhPc0QPozR1jDPPikyTq09o6v0SWp2Mp7+ufJ+2YQgDOpOJ02dwWjIW9pcvHRabD +Dqb+B3aq/0RCQfGwJeLKWgb83t/YH9Krned8rKGBxz7Kn1Prelotw28wszem76WHi 23S3wZ4CZaRq6FhF6OouBIIl2FaM1NXb+FRderwJ35YjB9PIWQY91i4HWJxHzK7oEY CDOfjMc3xPVWbPHj/ll9LuYaP2CxFu7OROpM7tpjN7jsvhIM/tG77GdUiHIoKFnBg9 SbND62Ma8llSQ== Message-ID: <98480065-e988-477f-ba37-f9521e4aecbb@kernel.org> Date: Mon, 2 Mar 2026 09:00:07 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/vmscan: restore allowed mask in alloc_demote_folio() To: Bing Jiao , linux-mm@kvack.org Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Axel Rasmussen , Yuanchu Xie , Wei Xu , linux-kernel@vger.kernel.org References: <20260302070351.3465439-1-bingjiao@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/2/26 08:03, Bing Jiao wrote: > In alloc_demote_folio(), mtc->nmask is set to NULL for the first > allocation. If that succeeds, it returns without restoring mtc->nmask > to allowed_mask. For subsequent allocations from the migrate_pages() > batch, mtc->nmask will be NULL. If the target node then becomes full, > the fallback allocation will use nmask = NULL, allocating from any > node allowed by the task cpuset, which for kswapd is all nodes. > > To address this issue, restore the mtc->nmask to its original allowed > nodemask after the first allocation. > That would be Fixes: 320080272892 ("mm/demotion: demote pages according to allocation fallback order") ? > Signed-off-by: Bing Jiao > --- > mm/vmscan.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index cbffc0a27824..b42abd17aee7 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -985,11 +985,11 @@ static struct folio *alloc_demote_folio(struct folio *src, > mtc->nmask = NULL; > mtc->gfp_mask |= __GFP_THISNODE; > dst = alloc_migration_target(src, (unsigned long)mtc); > + mtc->nmask = allowed_mask; > if (dst) > return dst; > > mtc->gfp_mask &= ~__GFP_THISNODE; > - mtc->nmask = allowed_mask; > > return alloc_migration_target(src, (unsigned long)mtc); > } > -- > 2.53.0.473.g4a7958ca14-goog > Maybe we should just not touch the original mtc? diff --git a/mm/vmscan.c b/mm/vmscan.c index de62225b381a..f07716e5389e 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -985,9 +985,9 @@ static void folio_check_dirty_writeback(struct folio *folio, static struct folio *alloc_demote_folio(struct folio *src, unsigned long private) { + struct migration_target_control *mtc, target_nid_mtc; struct folio *dst; nodemask_t *allowed_mask; - struct migration_target_control *mtc; mtc = (struct migration_target_control *)private; @@ -1001,15 +1001,12 @@ static struct folio *alloc_demote_folio(struct folio *src, * a demotion of cold pages from the target memtier. This can result * in the kernel placing hot pages in slower(lower) memory tiers. */ - mtc->nmask = NULL; - mtc->gfp_mask |= __GFP_THISNODE; - dst = alloc_migration_target(src, (unsigned long)mtc); + target_nid_mtc = *mtc; + target_nid_mtc.nmask = NULL; + target_nid_mtc.gfp_mask |= __GFP_THISNODE; + dst = alloc_migration_target(src, (unsigned long)&target_nid_mtc); if (dst) return dst; - - mtc->gfp_mask &= ~__GFP_THISNODE; - mtc->nmask = allowed_mask; - return alloc_migration_target(src, (unsigned long)mtc); } -- Cheers, David