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 408A64963C3 for ; Fri, 21 Aug 2026 14:18:37 +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=1787321919; cv=none; b=nNRxTFadWHbWSTn4eq10/vP7aj28qEZKU9yVI5nuueZKjxR4eLhYwwdz59zhzcfMuGotPtDbwxdMyR9d/eHy0Ftlokg+j0OZb7u6JNIF2lKkJKHvfV45EbM9vpJe1Edg+bPNqzdnMkep49Xx5+pcKEXJEnb4t3zDLwWE513K1Sk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787321919; c=relaxed/simple; bh=eVfWcsT7AWA+/dVY7TU+nPIQTV45CQDzFhWbDxxMiDI=; h=Message-ID:Date:MIME-Version:From:Subject:To:Cc:References: In-Reply-To:Content-Type; b=otwo+QJOOkouRPIzYFaUS8V7twA197xDOjqeTp648dYziW5REoyHUuBGabAMGB8paEQrow68YG4KN3fWz14V/BwUCAihX6ehZL0vuWBPkt/CHne+nVtG1n/A9fog4KNvqusiFihmh4xkT2raM3vG7LD5w5kMB4boRembsXI8x2I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mCrlU9qn; 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="mCrlU9qn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4B9141F000E9; Fri, 21 Aug 2026 14:18:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787321917; bh=25aRKT2H17E3+b7/M5uXvQXwb5OfRhehW7b7COK86RQ=; h=Date:From:Subject:To:Cc:References:In-Reply-To; b=mCrlU9qnLmCDoMjoYWy2y0kteLWFvhGmH4vE46dQiE+IlMGWWq8McDNVEzD9elWx3 juv4qEb/MC/XNLRAklmjfLHtMHpTTvfP7oFgME+Rhl27NzU6spRtGwNmfWK4EEyMqT 9t3bYLGlSPN9dEP7JKVf14K131nuy0Q27ZhwLWf09RqEwaiVKjfypqlxLrzG+VZn9V rO67iYJpwiEMYMyxDQi1csCNK9oWDQzBQMnxI41NR1WVZGTFszMidaaQcA26nTZMBo 6XmAJt7zrmAJTzv9Rogz+Ve8y2GeiqFxsBr2iucOrW+9M6FNqTwvnWC3DRDfNM48FF BQ9vTfkzJLoqg== Message-ID: Date: Fri, 21 Aug 2026 16:18:31 +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 From: "David Hildenbrand (Arm)" Subject: Re: [RFC PATCH v3 0/4] mm: enable lru cache for smaller large folios To: Barry Song Cc: akpm@linux-foundation.org, linux-mm@kvack.org, baolin.wang@linux.alibaba.com, dev.jain@arm.com, lance.yang@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, ljs@kernel.org, mhocko@suse.com, npache@redhat.com, rppt@kernel.org, ryan.roberts@arm.com, surenb@google.com, vbabka@kernel.org, ziy@nvidia.com, hughd@google.com, ackerleytng@google.com, usama.arif@linux.dev, joannelkoong@gmail.com, hannes@cmpxchg.org References: <20260818225904.55236-1-baohua@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 8/20/26 22:18, Barry Song wrote: > On Fri, Aug 21, 2026 at 2:23 AM David Hildenbrand (Arm) > wrote: >> >> On 8/19/26 00:59, Barry Song (Xiaomi) wrote: >>> This patchset enables the per-CPU LRU cache for large folios with fewer >>> than `FOLIO_BATCH_SIZE` (31) pages. It also limits each per-CPU LRU cache >>> to at most `FOLIO_BATCH_SIZE` pages to avoid negatively affecting >>> accounting and memory reclamation pressure. >>> >>> This is particularly beneficial on systems that use relatively small >>> large folios. For larger folios, the benefit is likely to be smaller >>> because far fewer folios are expected to contend for the LRU cache. >> >> As raised, there is this problem with collect_longterm_unpinnable_folios() >> >> (see >> https://lore.kernel.org/r/20260806-lru_cache_drain_for_folio-v1-1-c6287d295e99@kernel.org >> ) >> >> whereby we don't know how many refs we actually hold. Certainly not 1. >> >> We might have to wait for Hugh's cleanup to handle that cleanly (and avoid all >> the other LRU cache draining). > > Hi David, > Thanks for raising this. > Yes, I saw your comment and took a closer look at it. I think the > best approach for now is to leave that part untouched until Hugh's > patch lands? I think we should not consider your patch set until Hugh either resolved it or we have a better way to handle draining. Building on top of this for large folios now just gets painful. > We might end up doing some extra draining in that case, > but that's safe—any value greater than 1 might not be. We'll unconditionally drain all LRU caches, which is precisely *not* what we want to do in the first place. :) -- Cheers, David