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 X-Spam-Level: X-Spam-Status: No, score=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CA2A8C433DB for ; Mon, 11 Jan 2021 18:18:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 90EF6207B1 for ; Mon, 11 Jan 2021 18:18:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390400AbhAKSST (ORCPT ); Mon, 11 Jan 2021 13:18:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58728 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390056AbhAKSST (ORCPT ); Mon, 11 Jan 2021 13:18:19 -0500 Received: from mail-ej1-x62f.google.com (mail-ej1-x62f.google.com [IPv6:2a00:1450:4864:20::62f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DB0DDC061795; Mon, 11 Jan 2021 10:17:38 -0800 (PST) Received: by mail-ej1-x62f.google.com with SMTP id 6so995644ejz.5; Mon, 11 Jan 2021 10:17:38 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=/HR2yya3rEhjyoFHghdM9H+zzVIak5D+Mg99fwtlBy0=; b=uccSzMfhv+MJ/yyDhYaTeiciitkkoQrrtsZ38UW6OuSdnuG+c9uwmdYv+aXMbLfnVc +w3dcskYN9SbcJm+5q3Gdo55QIVI+MN/MbiWT6l5TodUBkGLl9qv1SmlsKhafi5S0ul2 1NGky+Qs6Fv7chzE9vjTXfPL1AopKwPjGK2Hl4t+WkpsJWAnO6Vt02PXX1/PFIZonFPo T/3cBWq6V1NALGOykqorxztCLXNZhG7yVBtvegIBlcjYYAhYjzIeRUhychQYgigqCN7I R8bKY7Cvdb7BgerA+3GEmlqniOhAk1gj71+O+QQ+PVUKOW7xs1x1NDtmNrPc8HNsmLoE lDjg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=/HR2yya3rEhjyoFHghdM9H+zzVIak5D+Mg99fwtlBy0=; b=QZlNsRJb66cciPUNEUtc+ERm71uBwvMSwzEAx8zMT97UACG81gavYuMIi8NjvH99pV gfgiM2sm9DC5NHYmn2Wh0c0XK1cgJaaWC31HOAtAS1nyl8ImdJpEGSwajfi+vJ0iCfSZ VG8S3QxbprZ0v5zn3+PMjdTsMWV8cXix6prVFNZpruRlU+TxmFAksq9ALpN7X7s02ojp W74AhvoZOJuSC4dbDEmWgjEA2ZvxZJ63IiqmM3ik7z/g2dq1+AETVnELRq3QYsYWnLlF ZXLjrd82Dmxxg1xSZPlLTe5nucleu8jmL/aJkdMEPkMAeUok913yeh49MdUFTmj9wzUi IFxA== X-Gm-Message-State: AOAM530KHP85UC6CoGyFwDpmo4neq5G32KSCY7v4MxzovJuzgdu5/T2U pscZdayMcmdegu4Ddsg36BsX+K7Hs+8RuhcgLFk= X-Google-Smtp-Source: ABdhPJyRyrzpvUSXDYm8hrLQbJY/N1WQX20rHB1kkjGw3lluI6obLTHbnob3FibmX03jboDaSvc89z5PWTXjHvr2r/A= X-Received: by 2002:a17:907:20a4:: with SMTP id pw4mr470797ejb.499.1610389057657; Mon, 11 Jan 2021 10:17:37 -0800 (PST) MIME-Version: 1.0 References: <20210105225817.1036378-1-shy828301@gmail.com> <20210105225817.1036378-6-shy828301@gmail.com> In-Reply-To: From: Yang Shi Date: Mon, 11 Jan 2021 10:17:25 -0800 Message-ID: Subject: Re: [v3 PATCH 05/11] mm: vmscan: use a new flag to indicate shrinker is registered To: Kirill Tkhai Cc: Roman Gushchin , Shakeel Butt , Dave Chinner , Johannes Weiner , Michal Hocko , Andrew Morton , Linux MM , Linux FS-devel Mailing List , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, Jan 6, 2021 at 2:22 AM Kirill Tkhai wrote: > > On 06.01.2021 01:58, Yang Shi wrote: > > Currently registered shrinker is indicated by non-NULL shrinker->nr_deferred. > > This approach is fine with nr_deferred at the shrinker level, but the following > > patches will move MEMCG_AWARE shrinkers' nr_deferred to memcg level, so their > > shrinker->nr_deferred would always be NULL. This would prevent the shrinkers > > from unregistering correctly. > > > > Signed-off-by: Yang Shi > > --- > > include/linux/shrinker.h | 7 ++++--- > > mm/vmscan.c | 13 +++++++++---- > > 2 files changed, 13 insertions(+), 7 deletions(-) > > > > diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h > > index 0f80123650e2..1eac79ce57d4 100644 > > --- a/include/linux/shrinker.h > > +++ b/include/linux/shrinker.h > > @@ -79,13 +79,14 @@ struct shrinker { > > #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */ > > > > /* Flags */ > > -#define SHRINKER_NUMA_AWARE (1 << 0) > > -#define SHRINKER_MEMCG_AWARE (1 << 1) > > +#define SHRINKER_REGISTERED (1 << 0) > > +#define SHRINKER_NUMA_AWARE (1 << 1) > > +#define SHRINKER_MEMCG_AWARE (1 << 2) > > /* > > * It just makes sense when the shrinker is also MEMCG_AWARE for now, > > * non-MEMCG_AWARE shrinker should not have this flag set. > > */ > > -#define SHRINKER_NONSLAB (1 << 2) > > +#define SHRINKER_NONSLAB (1 << 3) > > > > extern int prealloc_shrinker(struct shrinker *shrinker); > > extern void register_shrinker_prepared(struct shrinker *shrinker); > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 8da765a85569..9761c7c27412 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -494,6 +494,7 @@ void register_shrinker_prepared(struct shrinker *shrinker) > > if (shrinker->flags & SHRINKER_MEMCG_AWARE) > > idr_replace(&shrinker_idr, shrinker, shrinker->id); > > #endif > > + shrinker->flags |= SHRINKER_REGISTERED; > > In case of we introduce this new flag, we should kill old flag SHRINKER_REGISTERING, > which are not needed anymore (we should you the new flag instead of that). The only think that I'm confused with is the check in shrink_slab_memcg, it does: shrinker = idr_find(&shrinker_idr, i); if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) { When allocating idr, the shrinker is associated with SHRINKER_REGISTERING. But, shrink_slab_memcg does acquire read shrinker_rwsem, and idr_alloc is called with holding write shrinker_rwsem, so I'm supposed shrink_slab_memcg should never see shrinker is registering. If so it seems easy to remove SHRINKER_REGISTERING. We just need change that check to: !shrinker || !(shrinker->flags & SHRINKER_REGISTERED) > > up_write(&shrinker_rwsem); > > } > > > > @@ -513,13 +514,17 @@ EXPORT_SYMBOL(register_shrinker); > > */ > > void unregister_shrinker(struct shrinker *shrinker) > > { > > - if (!shrinker->nr_deferred) > > - return; > > - if (shrinker->flags & SHRINKER_MEMCG_AWARE) > > - unregister_memcg_shrinker(shrinker); > > down_write(&shrinker_rwsem); > > I do not think there are some users which registration may race with unregistration. > So, I think we should check SHRINKER_REGISTERED unlocked similar to we used to check > shrinker->nr_deferred unlocked. Yes, I agree. > > > + if (!(shrinker->flags & SHRINKER_REGISTERED)) { > > + up_write(&shrinker_rwsem); > > + return; > > + } > > list_del(&shrinker->list); > > + shrinker->flags &= ~SHRINKER_REGISTERED; > > up_write(&shrinker_rwsem); > > + > > + if (shrinker->flags & SHRINKER_MEMCG_AWARE) > > + unregister_memcg_shrinker(shrinker); > > kfree(shrinker->nr_deferred); > > shrinker->nr_deferred = NULL; > > } > > > >