From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7CDBEFF885C for ; Sat, 25 Apr 2026 05:34:48 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DC1AB6B008A; Sat, 25 Apr 2026 01:34:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D99536B008C; Sat, 25 Apr 2026 01:34:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CD5B26B0092; Sat, 25 Apr 2026 01:34:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id BABFA6B008A for ; Sat, 25 Apr 2026 01:34:47 -0400 (EDT) Received: from smtpin17.hostedemail.com (lb01b-stub [10.200.18.250]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 45E601A0279 for ; Sat, 25 Apr 2026 05:34:47 +0000 (UTC) X-FDA: 84695963814.17.B227D67 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) by imf03.hostedemail.com (Postfix) with ESMTP id 5493B20003 for ; Sat, 25 Apr 2026 05:34:45 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=LPLgtwEH; spf=pass (imf03.hostedemail.com: domain of jp.kobryn@linux.dev designates 91.218.175.179 as permitted sender) smtp.mailfrom=jp.kobryn@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1777095285; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:references:dkim-signature; bh=O2wKaLfeccrLPK9TR/V0xj0n49MCRpo9cMDPX1EG854=; b=SrQ5e6ZGuNmKPSuEkrDSvMk6p41SIkXM/d6Zr3xFNzH4LnTTQH4zJi+ypoQGPF2GP6Y3H0 xC2Zx6vx+3vIbNmGOlcqI2eTpFs5Mk4LwZx4HTupC+BG8DDV1mu57RldQCLI5O6tY/Q5CB tvZwPxnyOewnpTLD2gOtgGi54J9C7Us= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=LPLgtwEH; spf=pass (imf03.hostedemail.com: domain of jp.kobryn@linux.dev designates 91.218.175.179 as permitted sender) smtp.mailfrom=jp.kobryn@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1777095285; a=rsa-sha256; cv=none; b=qbBhHuvPBjG7q/B4QyxIx+if0kJ1O+vxXTfKWEO4Xd1Foj08zvrTCt8uZwduEMyppavxQy gIEIEgLCa0aBPokvbzHxuy/K4mhUqQUsfUqWTvd+57ZXwhk9J8QvDC2RZXbqoFVlFcSPCp jhNOC/yYmEdI7I52cIluRO/NbjRYGQo= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1777095282; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=O2wKaLfeccrLPK9TR/V0xj0n49MCRpo9cMDPX1EG854=; b=LPLgtwEHTOentynaddiLXYxSON7SMFqntHAFikcN7Vqdqn2HG7t5Ts2ILIacZ7fO/o3oz9 YyTiiUBTacaacPL6Xd5u8Ss8euxJvWRxA13+UJ++Fwu/SoalBEiTvf1SieXmXmdK3aIZhy pscxUbgSzsopGUj+tLs2KtG6AB+Vf88= From: "JP Kobryn (Meta)" To: linux-mm@kvack.org, akpm@linux-foundation.org, willy@infradead.org, baohua@kernel.org, mhocko@suse.com, vbabka@kernel.org, hannes@cmpxchg.org, shakeel.butt@linux.dev, 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 Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: [PATCH v2] mm/lruvec: preemptively free dead folios during lru_add drain Date: Fri, 24 Apr 2026 22:34:17 -0700 Message-ID: <20260425053417.351146-1-jp.kobryn@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: 7gw1aofnmcmijtbko9nanqu11p5c1ysw X-Rspamd-Queue-Id: 5493B20003 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1777095285-432458 X-HE-Meta: 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 rsogaDQo dhVqjDReFsylvTOUjPTrUvXG5BWrD3UynyIaL6M6XDQBS6KpuDNlb+sf08URVdpu7fUO5ULcyfKp0o+SQ718YgPDwY7kqZmPqjOAnuXw0qPxADyKUwqyJmEaIluvtB43MazjT/Wwb56bKs3ktN7fGWgFsL7VetClytJg3GSlPNsYU19+/iBwrlyBGA9yE89NqoR3AURISem6mJ/dEWeNr9WA6fzZrhO0inKsL5WTWyFcc4WOsRTQWhPmSn0d7hUnbZpUADYvIgHXaCNz/WIwH2ixNjcGTu+8LbWK2gpruUHVjdaK5CQ9rL+/VuPhMG6PwUmNUAI/pjWOWPVgZFj4LA+54Uy1pXMjzIo0C6YLWxk8VR5xLAjwQ9IawPUO/8r4lj3+uQkpH41od4FE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. PG_active may be set on a batched folio as well as PG_unevictable (via migration path). Since filtered folios bypass the normal lru_add() cleanup, both flags must be cleared before freeing. 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%). Note that tests were performed using classic LRU. Signed-off-by: JP Kobryn (Meta) Reviewed-by: Matthew Wilcox (Oracle) Acked-by: Shakeel Butt Acked-by: Michal Hocko --- v2 - clear PG_active and PG_unevictable flags before adding to free batch v1: https://lore.kernel.org/linux-mm/20260423164307.29805-1-jp.kobryn@linux.dev/ mm/swap.c | 41 ++++++++++++++++++++++++++++++++++++++++- 1 file changed, 40 insertions(+), 1 deletion(-) diff --git a/mm/swap.c b/mm/swap.c index 5cc44f0de9877..2dd84813f4dde 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -160,14 +160,42 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) int i; struct lruvec *lruvec = NULL; unsigned long flags = 0; + struct folio_batch free_fbatch; + bool is_lru_add = (move_fn == lru_add); + + /* + * If we're adding to the LRU, preemptively filter dead folios. Use + * this dedicated folio batch for temp storage and deferred cleanup. + */ + if (is_lru_add) + folio_batch_init(&free_fbatch); for (i = 0; i < folio_batch_count(fbatch); i++) { struct folio *folio = fbatch->folios[i]; /* block memcg migration while the folio moves between lru */ - if (move_fn != lru_add && !folio_test_clear_lru(folio)) + if (!is_lru_add && !folio_test_clear_lru(folio)) continue; + /* + * Filter dead folios by moving them from the add batch to the temp + * batch for freeing after this loop. + * + * We're bypassing normal cleanup. Clear flags that are not + * applicable to dead folios. + * + * Since the folio may be part of a huge page, unqueue from + * deferred split list to avoid a dangling list entry. + */ + if (is_lru_add && folio_ref_freeze(folio, 1)) { + __folio_clear_active(folio); + __folio_clear_unevictable(folio); + folio_unqueue_deferred_split(folio); + fbatch->folios[i] = NULL; + folio_batch_add(&free_fbatch, folio); + continue; + } + folio_lruvec_relock_irqsave(folio, &lruvec, &flags); move_fn(lruvec, folio); @@ -176,6 +204,13 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) if (lruvec) lruvec_unlock_irqrestore(lruvec, flags); + + /* Cleanup filtered dead folios. */ + if (is_lru_add) { + mem_cgroup_uncharge_folios(&free_fbatch); + free_unref_folios(&free_fbatch); + } + folios_put(fbatch); } @@ -964,6 +999,10 @@ void folios_put_refs(struct folio_batch *folios, unsigned int *refs) struct folio *folio = folios->folios[i]; unsigned int nr_refs = refs ? refs[i] : 1; + /* Folio batch entry may have been preemptively removed during drain. */ + if (!folio) + continue; + if (is_huge_zero_folio(folio)) continue; -- 2.52.0