From nobody Tue Sep 9 21:31:45 2025 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 20E88C77B61 for ; Thu, 13 Apr 2023 10:40:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230355AbjDMKkt (ORCPT ); Thu, 13 Apr 2023 06:40:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50708 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230116AbjDMKkk (ORCPT ); Thu, 13 Apr 2023 06:40:40 -0400 Received: from mail-pl1-x64a.google.com (mail-pl1-x64a.google.com [IPv6:2607:f8b0:4864:20::64a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 418D0E64 for ; Thu, 13 Apr 2023 03:40:39 -0700 (PDT) Received: by mail-pl1-x64a.google.com with SMTP id z9-20020a170903018900b001a1e8390831so7846008plg.5 for ; Thu, 13 Apr 2023 03:40:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1681382439; x=1683974439; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=xGnocY4pIBEOyCy1J5p5K30k0wCvlbaawbxDP+ACQr8=; b=7DaELoYbwDJCrNtZlmfg9Wt1StcR4uFr/DcPD/2pe3cLhlNGHN0Vo/cQ7EdPJo7up0 8bmCI0JQEmCL566Vot7ySRXaEZ0Q9wHFt3Sh9NvXD+gSBVNkrXxQorzAPrPz3sL21Jvg UkLNapMN9bhRXj3lO4/bDPz8UGmnAz0jlApmptNFgfyGVpKdYVctpDwfppNvGRrl4WXx hDn5QBpGHzMAOlfKXhd4xxjuLNGoae6rpvwcD9uDypxIntJ4NI1CR6tegrXbWE9t7vA4 LHSI7L2dX5euMSDWQaeHCt4S6p/b4GKxns2a9UeAtjH7MQxy0QVqfkDsaHQMGS5XAPuo 907w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1681382439; x=1683974439; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=xGnocY4pIBEOyCy1J5p5K30k0wCvlbaawbxDP+ACQr8=; b=LWgzxlDNYAY11e1+vFijxLu+9+rIXSbWT2z7xT+ZVODAWxI205nruvKM87Wal5k3hr QrcNgvI1guwkVO3UYkPiR0HnNlK6qXPBuGCp/AbPUPoPDPHVdQTQQsXIoHds63TxkMeJ L/JcdmljFKSi7fPf2nLjlSq4elT2yfOBZ8HhPbM580gXE+Jm06xZdrP0lgYT46Fo4fSV YeyMlcd23UU0skKAdswtpnjwZnTJLhhCZ7GkoKkh6cMd4zxJxJ+RNMRmTdPqUAUuEFOa wUqZb9wtxMpeUatRukWfw8ZU085v94uF/2HwyRIprar0vitQwsO75LYvvSEm0d6mLox+ hm9A== X-Gm-Message-State: AAQBX9d2eeCLTN1V66KWRjmrtOQ0YNtwB1WXkjl5DwVKXrcsrxN2Gqw2 Jc1USN3ntTFFDyQ926cQRb80TTjE4Kl7wIXM X-Google-Smtp-Source: AKy350a/CmtWydI2qt+GCIKlEW3m+RGe6OazzLUzw02C2znW4S1CHo0XCY6i4wYnjhyCBrNF8AH/yKwjvGLojZVt X-Received: from yosry.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:2327]) (user=yosryahmed job=sendgmr) by 2002:a65:51c7:0:b0:51a:f873:2645 with SMTP id i7-20020a6551c7000000b0051af8732645mr331971pgq.9.1681382438784; Thu, 13 Apr 2023 03:40:38 -0700 (PDT) Date: Thu, 13 Apr 2023 10:40:32 +0000 In-Reply-To: <20230413104034.1086717-1-yosryahmed@google.com> Mime-Version: 1.0 References: <20230413104034.1086717-1-yosryahmed@google.com> X-Mailer: git-send-email 2.40.0.577.gac1e443424-goog Message-ID: <20230413104034.1086717-2-yosryahmed@google.com> Subject: [PATCH v6 1/3] mm: vmscan: ignore non-LRU-based reclaim in memcg reclaim From: Yosry Ahmed To: Andrew Morton , Alexander Viro , "Darrick J. Wong" , Christoph Lameter , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, "Matthew Wilcox (Oracle)" , Miaohe Lin , David Hildenbrand , Johannes Weiner , Peter Xu , NeilBrown , Shakeel Butt , Michal Hocko , Yu Zhao , Dave Chinner , Tim Chen Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-mm@kvack.org, Yosry Ahmed Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" We keep track of different types of reclaimed pages through reclaim_state->reclaimed_slab, and we add them to the reported number of reclaimed pages. For non-memcg reclaim, this makes sense. For memcg reclaim, we have no clue if those pages are charged to the memcg under reclaim. Slab pages are shared by different memcgs, so a freed slab page may have only been partially charged to the memcg under reclaim. The same goes for clean file pages from pruned inodes (on highmem systems) or xfs buffer pages, there is no simple way to currently link them to the memcg under reclaim. Stop reporting those freed pages as reclaimed pages during memcg reclaim. This should make the return value of writing to memory.reclaim, and may help reduce unnecessary reclaim retries during memcg charging. Writing to memory.reclaim on the root memcg is considered as cgroup_reclaim(), but for this case we want to include any freed pages, so use the global_reclaim() check instead of !cgroup_reclaim(). Generally, this should make the return value of try_to_free_mem_cgroup_pages() more accurate. In some limited cases (e.g. freed a slab page that was mostly charged to the memcg under reclaim), the return value of try_to_free_mem_cgroup_pages() can be underestimated, but this should be fine. The freed pages will be uncharged anyway, and we can charge the memcg the next time around as we usually do memcg reclaim in a retry loop. Fixes: f2fe7b09a52b ("mm: memcg/slab: charge individual slab objects instead of pages") Signed-off-by: Yosry Ahmed Acked-by: David Hildenbrand Acked-by: Michal Hocko --- mm/vmscan.c | 49 ++++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 42 insertions(+), 7 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 9c1c5e8b24b8..be657832be48 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -511,6 +511,46 @@ static bool writeback_throttling_sane(struct scan_cont= rol *sc) } #endif =20 +/* + * flush_reclaim_state(): add pages reclaimed outside of LRU-based reclaim= to + * scan_control->nr_reclaimed. + */ +static void flush_reclaim_state(struct scan_control *sc) +{ + /* + * Currently, reclaim_state->reclaimed includes three types of pages + * freed outside of vmscan: + * (1) Slab pages. + * (2) Clean file pages from pruned inodes (on highmem systems). + * (3) XFS freed buffer pages. + * + * For all of these cases, we cannot universally link the pages to a + * single memcg. For example, a memcg-aware shrinker can free one object + * charged to the target memcg, causing an entire page to be freed. + * If we count the entire page as reclaimed from the memcg, we end up + * overestimating the reclaimed amount (potentially under-reclaiming). + * + * Only count such pages for global reclaim to prevent under-reclaiming + * from the target memcg; preventing unnecessary retries during memcg + * charging and false positives from proactive reclaim. + * + * For uncommon cases where the freed pages were actually mostly + * charged to the target memcg, we end up underestimating the reclaimed + * amount. This should be fine. The freed pages will be uncharged + * anyway, even if they are not counted here properly, and we will be + * able to make forward progress in charging (which is usually in a + * retry loop). + * + * We can go one step further, and report the uncharged objcg pages in + * memcg reclaim, to make reporting more accurate and reduce + * underestimation, but it's probably not worth the complexity for now. + */ + if (current->reclaim_state && global_reclaim(sc)) { + sc->nr_reclaimed +=3D current->reclaim_state->reclaimed; + current->reclaim_state->reclaimed =3D 0; + } +} + static long xchg_nr_deferred(struct shrinker *shrinker, struct shrink_control *sc) { @@ -5346,8 +5386,7 @@ static int shrink_one(struct lruvec *lruvec, struct s= can_control *sc) vmpressure(sc->gfp_mask, memcg, false, sc->nr_scanned - scanned, sc->nr_reclaimed - reclaimed); =20 - sc->nr_reclaimed +=3D current->reclaim_state->reclaimed_slab; - current->reclaim_state->reclaimed_slab =3D 0; + flush_reclaim_state(sc); =20 return success ? MEMCG_LRU_YOUNG : 0; } @@ -6450,7 +6489,6 @@ static void shrink_node_memcgs(pg_data_t *pgdat, stru= ct scan_control *sc) =20 static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) { - struct reclaim_state *reclaim_state =3D current->reclaim_state; unsigned long nr_reclaimed, nr_scanned; struct lruvec *target_lruvec; bool reclaimable =3D false; @@ -6472,10 +6510,7 @@ static void shrink_node(pg_data_t *pgdat, struct sca= n_control *sc) =20 shrink_node_memcgs(pgdat, sc); =20 - if (reclaim_state) { - sc->nr_reclaimed +=3D reclaim_state->reclaimed_slab; - reclaim_state->reclaimed_slab =3D 0; - } + flush_reclaim_state(sc); =20 /* Record the subtree's reclaim efficiency */ if (!sc->proactive) --=20 2.40.0.577.gac1e443424-goog