From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 19D6232B9B5; Wed, 22 Jul 2026 12:18:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784722682; cv=none; b=XypbPkPT79TLyBXPLO+93uOg153/jYPnqSKP8erwVStgrxj8/9he6kThbTVv0M4byUdhA0kq/9wYst7kRizf/rqucR9gfB0B1pGK1cp+RdJP9bjwreG8oIp449HCQnsI90y3HWCmkOaKZFNUNfXdVKP9T3wqlmWKZ8I8As9ycRs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784722682; c=relaxed/simple; bh=F4jKDdyt9nnUyq8d21IZO/6Lc7qTAXK58nfG02soCrs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HKxGtMFQYlQ+S3fHzZSJVbTIBDTGAF/REiAl7uiAuW+d4YCZP5jcFptMybzQA2AU0WHen4Ecb/4/I4UtNkpa2ub1Y1Q4VCqKFSMTGggZK0GrwchXxy9e2DqBWRVnk9iZNsi2FYdoOcEpQ8ZG3XxRKpIDPp7f83/9deBknf335iA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=llzUFJes; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="llzUFJes" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A52A11F000E9; Wed, 22 Jul 2026 12:17:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784722680; bh=quxgKTCBV0BCb8OJSz8QFDvBn14uAzUBItc9eXawEb8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=llzUFJesRwmmjClmGbFEABpUrAxWeJ8td+4hi1QIL4JNVvi/XNe8d3RjuNnACVrW/ 7hle8tPvlOSc+w1wiutgzm18ZZfTO8qvDXB65un7N68GFVCqsCsq66DfkYhq8scZfR 6sZDMvuJryibh2cvMZal61Dcu/s5hOtKYL2k2VN4rgYVQga6JTq4NBXkQcasPJzDVB y6YmNHjBBOjH+GFOqdlOIRsaJe+blbSekhtDkT1JtR8e0hHkhM2IZ8ufMfULVN4XU6 vxxKuQj2Sr4CHPRvr1AyMWXny34u05KxGegwnmtP66C1iCFPpDWL2CL9Jp1MOFs1oV PU9dr6VTe2bKg== Message-ID: <15c65a4b-aa53-4218-baa4-7dbab3b9dbab@kernel.org> Date: Wed, 22 Jul 2026 14:17:54 +0200 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 v3] mm/page_alloc: avoid direct compaction for costly __GFP_NORETRY allocations Content-Language: en-US To: Matthew Wilcox , Salvatore Dipietro Cc: linux-mm@kvack.org, hch@infradead.org, ritesh.list@gmail.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, dgc@kernel.org, djwong@kernel.org, brauner@kernel.org, alisaidi@amazon.com, blakgeof@amazon.com, abuehaze@amazon.com, dipietro.salvatore@gmail.com, stable@vger.kernel.org, Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan References: <20260710143437.12379-1-dipiets@amazon.it> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/10/26 20:03, Matthew Wilcox wrote: > On Fri, Jul 10, 2026 at 02:34:37PM +0000, Salvatore Dipietro wrote: >> Commit 5d8edfb900d5 ("iomap: Copy larger chunks from userspace") >> introduced high-order folio allocations in the iomap buffered write >> path. > > https://lore.kernel.org/linux-mm/aeZzP6iQel-tkZOu@casper.infradead.org/ > > I just had a go at implementing what I thought might be the right design > (having a folio_alloc_orders(min, max, gfp)), but that's not really what > __filemap_get_folio_mpol() wants because it needs to integrate the actual > adding of folios to the page cache into the retry loop. > > So instead, let's try this. The idea is that we want to try direct reclaim > _twice_. Once gently (ie with NORETRY specified) when we're trying to > allocate the maximum order folio. But now that we've tried that once, > there's no point trying direct reclaim for other sizes, we just want to > ask the page allocator if it can give us memory of any subsequent size. > > Until we come to the minimum order. Then we want to try exactly as hard > as we were originally asked to try. So revert to the original gfp flags > and don't set the NOWARN or NORETRY flags. > > diff --git a/mm/filemap.c b/mm/filemap.c > index 58eb9d240643..23eecaf9b328 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -1983,6 +1983,7 @@ struct folio *__filemap_get_folio_mpol(struct address_space *mapping, > if (!folio && (fgp_flags & FGP_CREAT)) { > unsigned int min_order = mapping_min_folio_order(mapping); > unsigned int order = max(min_order, FGF_GET_ORDER(fgp_flags)); > + gfp_t alloc_gfp = gfp | __GFP_NORETRY | __GFP_NOWARN; > int err; > index = mapping_align_index(mapping, index); Note here fgp_flags are checked and may alter gfp towards NOFS or NOWAIT or add __GFP_WRITE. But alloc_gfp set above will ignore all that for >min_order attempts, which isn't right. Probably doesn't affect Salvatore's evaluation though. > @@ -2004,12 +2005,11 @@ struct folio *__filemap_get_folio_mpol(struct address_space *mapping, > order = __ffs(index); > > do { > - gfp_t alloc_gfp = gfp; > - > err = -ENOMEM; > - if (order > min_order) > - alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN; > + if (order == min_order) > + alloc_gfp = gfp; > folio = filemap_alloc_folio(alloc_gfp, order, policy); > + alloc_gfp &= ~__GFP_DIRECT_RECLAIM; > if (!folio) > continue; >