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=ham 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 4D3D9C433DB for ; Tue, 12 Jan 2021 20:58:25 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id BA5442311A for ; Tue, 12 Jan 2021 20:58:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BA5442311A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1B8DE6B00D6; Tue, 12 Jan 2021 15:58:24 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 143DE6B00D8; Tue, 12 Jan 2021 15:58:24 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 031A76B00D9; Tue, 12 Jan 2021 15:58:23 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0046.hostedemail.com [216.40.44.46]) by kanga.kvack.org (Postfix) with ESMTP id DCD286B00D6 for ; Tue, 12 Jan 2021 15:58:23 -0500 (EST) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 9C8E3180AD801 for ; Tue, 12 Jan 2021 20:58:23 +0000 (UTC) X-FDA: 77698336086.16.suit27_280b85627518 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin16.hostedemail.com (Postfix) with ESMTP id 7BDBD100E6903 for ; Tue, 12 Jan 2021 20:58:23 +0000 (UTC) X-HE-Tag: suit27_280b85627518 X-Filterd-Recvd-Size: 7664 Received: from mail-ej1-f49.google.com (mail-ej1-f49.google.com [209.85.218.49]) by imf36.hostedemail.com (Postfix) with ESMTP for ; Tue, 12 Jan 2021 20:58:22 +0000 (UTC) Received: by mail-ej1-f49.google.com with SMTP id 6so5470527ejz.5 for ; Tue, 12 Jan 2021 12:58:22 -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=2488YfIKw2/IPkOU3jNJR+xLgk8bwBEm0EMuKAKYdtE=; b=r+7U1RgXJGA5UAOTqwDP6UL0+Qi7sfZ73exStFoFDpTEiR6aKOE5DcB5y6NaDIlH7W 9eb4xzc9BLBdVVNB5eTriTQMOmGqaA+uEuASwVTCHuUeeqJA4wMAw/o9sYpHRMpv4FHC K24MzipXIz4HRSsDVeBnNjd75HEf2tP3lYmDUJJtg9dnq69AaKvc3uA0PKvZMC847DzF 4qBpMwiInB5opME2tonWYmB9vo7vVBTxxls3tDZRpPQROsfvWRVZPeyAtDxrwEvhVyp6 f+gyJJFejYSdW6pkitd/La9X5P+E/R0FTVxLOIFs1j1vJGDymh5xJQHsutbcLwhljkUb XbeQ== 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=2488YfIKw2/IPkOU3jNJR+xLgk8bwBEm0EMuKAKYdtE=; b=WBNIt5PTzaz5s7dTnKj/J0OnSSkncuwNMEaMRUYsIYpTFgoIkOV3WbIRL6BCs/NM6a lHXIG4tbA8dJcNIDOtaPUBDYzLR1Zc/DAAWnvYMWS0iQFFzFkSdjqzv8vMEFUA9SiXni gGo+gg4Z78B5cleXE8xHn12BToqubvmuS7DAGxsgZeK8TBV9SbFFB52rqw54AJrWcKOu XrkE+rfDz3lK1XcPNfLvRh+NiIsWYroRKzMlYGBmm4DX0IjOWFCGIp5fu2oUx/ZpadLL bE3iE0/Ny/ukVzw98gn4uJUFTOXzcLPHWVa9xJKxggzgfSiIsoyI1z6dWkm2/1I/lT70 4C9Q== X-Gm-Message-State: AOAM531DVZvzCK6B7R1s4XY+jcOQB53Uc4qyOk/WHEZxX4mNWpjc2i8G fkNc4exq9lML1txIAkePefPCBjv+IeAWQRgD9WI= X-Google-Smtp-Source: ABdhPJywiChfAqj+hTD+lWNPDRLSpKCj8jiEW6HWfM7CeSy44afF60mxJ8fD+ZgkFhrLb+rqeT2kS7vvOifHe5uef6U= X-Received: by 2002:a17:906:6a45:: with SMTP id n5mr486085ejs.514.1610485101796; Tue, 12 Jan 2021 12:58:21 -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: Tue, 12 Jan 2021 12:58:10 -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" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jan 11, 2021 at 1:38 PM Kirill Tkhai wrote: > > On 11.01.2021 21:17, Yang Shi wrote: > > 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. > > After prealloc_shrinker() shrinker is visible for shrink_slab_memcg(). > This is the moment shrink_slab_memcg() sees SHRINKER_REGISTERED. Yes, this exactly is what I'm supposed. > > > 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; > >>> } > >>> > >> > >> > >