From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) (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 269D03CFF44 for ; Thu, 28 May 2026 15:31:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779982316; cv=none; b=B+XPvFzhVdwUr/yW0EFt/GxUR0FbO1aQ7shU/IbPEyX9udrcvd4ifTQdwAjg+ZmflAYlIiyWjB9hjgYiXUtK6yGmplUZSYsG2zdsB+/NmFitJO7NrE2Icosx0kFcE9vE0TFljWtpn+zOVQsjNCVYx0Ey3GnojLLW2hiDv3/L2YY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779982316; c=relaxed/simple; bh=+ce89fgs46k+cg+2rhqW6yHjRBW+INQCWV3V8lPGpRI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gh3XRa3G4yzc/RTQk5o5YujRdDWpkXvlrbYXcZPUtjL8NxL9gyys9rvyE6CP4usDDT1jAAO9MPNkznuISr1ZkZACz5dB4MlK4o25JBnvVl0102t+0Ybd8snGGBuJvFL/NsQ0XW19UqOLijSZxB3XCnOhvFlTYSVwaPyMYoVULsw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=cx4hFQ29; arc=none smtp.client-ip=95.215.58.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="cx4hFQ29" Message-ID: <6c138c46-9ef5-4dab-b65f-53f644b507d6@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1779982312; h=from:from: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; bh=J1oUqKehXs+Ix+t66SPeM6NBPV9gb1+9jfmojtKA5LI=; b=cx4hFQ29ac85axRefP3M5Zn1R7OcYorIPr7yFgQnJSKJP+xteuaLDNny5Wlt35GhtLJprE tYA/Fs8ehAM4OMZWLWihC59axuJa1+jn4WFbuVBq1573THJ7V92ueZ/8f7B/zqhTqx5bW9 WiTQyUk1NeVjWUfngkYaAwp3pIhOysE= Date: Thu, 28 May 2026 16:31:32 +0100 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v5 9/9] mm: switch deferred split shrinker to list_lru To: Johannes Weiner Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Shakeel Butt , Michal Hocko , Dave Chinner , Roman Gushchin , Muchun Song , Qi Zheng , Yosry Ahmed , Zi Yan , "Liam R . Howlett" , Kiryl Shutsemau , Vlastimil Babka , Kairui Song , Mikhail Zaslonko , Vasily Gorbik , Baolin Wang , Barry Song , Dev Jain , Lance Yang , Nico Pache , Ryan Roberts , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260527204757.2544958-1-hannes@cmpxchg.org> <20260527204757.2544958-10-hannes@cmpxchg.org> <6f9c78b2-3846-4f75-bcc2-41bf91230513@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Usama Arif In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 28/05/2026 15:02, Johannes Weiner wrote: > On Thu, May 28, 2026 at 02:32:06PM +0100, Usama Arif wrote: >> >> >> On 27/05/2026 21:45, Johannes Weiner wrote: >>> The deferred split queue handles cgroups in a suboptimal fashion. The >>> queue is per-NUMA node or per-cgroup, not the intersection. That means >>> on a cgrouped system, a node-restricted allocation entering reclaim >>> can end up splitting large pages on other nodes: >>> >>> alloc/unmap >>> deferred_split_folio() >>> list_add_tail(memcg->split_queue) >>> set_shrinker_bit(memcg, node, deferred_shrinker_id) >>> >>> for_each_zone_zonelist_nodemask(restricted_nodes) >>> mem_cgroup_iter() >>> shrink_slab(node, memcg) >>> shrink_slab_memcg(node, memcg) >>> if test_shrinker_bit(memcg, node, deferred_shrinker_id) >>> deferred_split_scan() >>> walks memcg->split_queue >>> >>> The shrinker bit adds an imperfect guard rail. As soon as the cgroup >>> has a single large page on the node of interest, all large pages owned >>> by that memcg, including those on other nodes, will be split. >>> >>> list_lru properly sets up per-node, per-cgroup lists. As a bonus, it >>> streamlines a lot of the list operations and reclaim walks. It's used >>> widely by other major shrinkers already. Convert the deferred split >>> queue as well. >>> >>> The list_lru per-memcg heads are instantiated on demand when the first >>> object of interest is allocated for a cgroup, by calling >>> folio_memcg_alloc_deferred(). Add calls to where splittable pages are >>> created: anon faults, swapin faults, khugepaged collapse. >>> >>> These calls create all possible node heads for the cgroup at once, so >>> the migration code (between nodes) doesn't need any special care. >>> >>> Reported-by: Mikhail Zaslonko >>> Tested-by: Mikhail Zaslonko >>> Acked-by: Shakeel Butt >>> Reviewed-by: Lorenzo Stoakes (Oracle) >>> Signed-off-by: Johannes Weiner >>> --- >>> include/linux/huge_mm.h | 7 +- >>> include/linux/memcontrol.h | 4 - >>> include/linux/mmzone.h | 12 -- >>> mm/huge_memory.c | 364 +++++++++++++------------------------ >>> mm/internal.h | 2 +- >>> mm/khugepaged.c | 5 + >>> mm/memcontrol.c | 12 +- >>> mm/memory.c | 4 + >>> mm/mm_init.c | 15 -- >>> mm/swap_state.c | 10 + >>> 10 files changed, 150 insertions(+), 285 deletions(-) >>> >> >> [...] >> >>> diff --git a/mm/memory.c b/mm/memory.c >>> index 135f5c0f57bd..f22e61d8c8de 100644 >>> --- a/mm/memory.c >>> +++ b/mm/memory.c >>> @@ -5222,6 +5222,10 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf) >>> folio_put(folio); >>> goto next; >>> } >>> + if (order > 1 && folio_memcg_alloc_deferred(folio)) { >>> + folio_put(folio); >> >> Ah sorry, should have caught this in the previous version, do we need >> >> count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK); >> >> here? > > This isn't an allocation we expect to fail with any sort of routine > that we'd need to capture it in the event counter. It would warn in > dmesg if it did. But in practice it can't happen at all, since it's a > sub-costly-order slab allocation and the allocator would loop and OOM > kill stuff until it succeeds. > >> or maybe we just goto next instead of goto fallback and trty next >> viable order? > > Again I don't think it matters, but fallback seems a bit more correct > because the size of the list_lru allocation doesn't change with lower > orders (until we hit 0). > > So I think we can just leave it as is. Ack! Acked-by: Usama Arif