From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) (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 828B73C3452 for ; Fri, 24 Apr 2026 15:38:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777045098; cv=none; b=XbLbzSine51g+K+iKI/StRzwi0jnrPR4HNTCt6XvpRcXVgtMndHTxU7TxCgoQY4SlZa9CK2Rj8tDnpuHYyIvSo/8WEsdx8n2b07M0M/Zu5F8fsT9GMiBOtBop/L7r/GISKbh31fgZy2rhco+8ETgdB6LBlSKlgtmU1jkLOnEoGo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777045098; c=relaxed/simple; bh=/EIPbMLvtv3puvPQ2QjYS2LSGvsHfboVnOdbKKOram4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YMrLqJJdOjZX0bnlSWSF60r5sKH5AiJKWkPsk8aL4K8skjhTdQSdV0X73d30V3r+QJtqjw3/Nh+bLrDbcbuTx+zm76/sCyX4DWtvw4CU/qbUe8lu3KgtlrRC34FBfaC7PwBLG++r6RTrbn69nhGEdbOKWTr0jq9v8t07rGnL3Fo= 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=gc01UbS1; arc=none smtp.client-ip=91.218.175.173 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="gc01UbS1" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1777045093; 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=zKN6v9bTjDgu0IaG/MSAwW/NKUa2Ct+xds0UCRCsb2c=; b=gc01UbS19yK1by58PvOyc4eS5trp09R5wDt5hf4nlod7Ef7qA8rZ+Z/wcXaYPd2QmVQXSc E59QoPSmF5tLGx9wQB4OaYYcA2CxwgitLcmv9YSPNW9Bqn3ai7rArwSUo8zhNZCvZ6Rnf5 tXvVqFzfzbe58uiCPeZCRNDcWqkI3M8= Date: Fri, 24 Apr 2026 08:38:06 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] mm/lruvec: preemptively free dead folios during lru_add drain To: Barry Song , Shakeel Butt Cc: linux-mm@kvack.org, akpm@linux-foundation.org, vbabka@kernel.org, mhocko@suse.com, willy@infradead.org, hannes@cmpxchg.org, riel@surriel.com, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, qi.zheng@linux.dev, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20260423164307.29805-1-jp.kobryn@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: "JP Kobryn (Meta)" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 4/23/26 4:53 PM, Barry Song wrote: > On Fri, Apr 24, 2026 at 7:46 AM Shakeel Butt wrote: >> >> On Fri, Apr 24, 2026 at 07:22:30AM +0800, Barry Song wrote: >>> On Fri, Apr 24, 2026 at 12:43 AM JP Kobryn (Meta) wrote: >>>> >>>> Of all observable lruvec lock contention in our fleet, we find that ~24% >>>> occurs when dead folios are present in lru_add batches at drain time. This >>>> is wasteful in the sense that the folio is added to the LRU just to be >>>> immediately removed via folios_put_refs(), incurring two unnecessary lock >>>> acquisitions. >>>> >>>> Eliminate this overhead by preemptively cleaning up dead folios before they >>>> make it into the LRU. Use folio_ref_freeze() to filter folios whose only >>>> remaining refcount is the batch ref. When dead folios are found, move them >>>> off the add batch and onto a temporary batch to be freed. >>>> >>>> During A/B testing on one of our prod instagram workloads (high-frequency >>>> short-lived requests), the patch intercepted almost all dead folios before >>>> they entered the LRU. Data collected using the mm_lru_insertion tracepoint >>>> shows the effectiveness of the patch: >>>> >>>> Per-host LRU add averages at 95% CPU load >>>> (60 hosts each side, 3 x 60s intervals) >>>> >>>> dead folios/min total folios/min dead % >>>> unpatched: 1,297,785 19,341,986 6.7097% >>>> patched: 14 19,039,996 0.0001% >>>> >>>> Within this workload, we save ~2.6M lock acquisitions per minute per host >>>> as a result. >>>> >>>> System-wide memory stats improved on the patched side also at 95% CPU load: >>>> - direct reclaim scanning reduced 7% >>>> - allocation stalls reduced 5.2% >>>> - compaction stalls reduced 12.3% >>>> - page frees reduced 4.9% >>>> >>>> No regressions were observed in requests served per second or request tail >>>> latency (p99). Both metrics showed directional improvement at higher CPU >>>> utilization (comparing 85% to 95%). >>>> >>>> Signed-off-by: JP Kobryn (Meta) >>> >>> Hi JP, >>> I’m seeing a large number of "BAD page" bugs. >>> Not sure if it’s related, but reverting this patch >>> seems to fix the issue. >>> >>> [ 2869.365978] BUG: Bad page state in process uname pfn:3a5417 >>> [ 2869.365981] page: refcount:0 mapcount:0 mapping:0000000000000000 >>> index:0x724884c20 pfn:0x3a5417 >>> [ 2869.365983] flags: >>> 0x17ffffc0020908(uptodate|active|owner_2|swapbacked|node=0|zone=2|lastcpupid=0x1fffff) >> >> Hi Barry, are you using MGLRU? It seems like MGLRU set active flag in >> folio_add_lru(). > > Yes. If you are referring to this set_active, I think it is > incorrect, so I have fixed it here and am waiting for review: > > https://lore.kernel.org/linux-mm/20260418120233.7162-1-baohua@kernel.org/ > >> >> JP, we need to clean active flag but let's check what else can be set before >> folio_add_lru(). Barry/Shakeel, We can do something like this as a special case for MGLRU: diff --git a/mm/swap.c b/mm/swap.c index 71607b0ce3d18..68ea929f65031 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -185,6 +185,8 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) * deferred split list to avoid a dangling list entry. */ if (is_lru_add && folio_ref_freeze(folio, 1)) { + if (lru_gen_enabled()) + __folio_clear_active(folio); folio_unqueue_deferred_split(folio); fbatch->folios[i] = NULL; folio_batch_add(&free_fbatch, folio); Unless Barry's patch works out... Any thoughts?