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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A0FF0ECAAD1 for ; Thu, 1 Sep 2022 10:01:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233523AbiIAKBa (ORCPT ); Thu, 1 Sep 2022 06:01:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39636 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233301AbiIAKBY (ORCPT ); Thu, 1 Sep 2022 06:01:24 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1EB86134898 for ; Thu, 1 Sep 2022 03:01:22 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id C7512219F1; Thu, 1 Sep 2022 10:01:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1662026480; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=pUkZJWp2nQ4dbOBqWBuaF5RJwLtyXngvDW9UF32VZDE=; b=qKa4+SljwPi5zCaniT9NpUQnkosVRVt7giTvOKUpwsXKorMmAxQewzjtYbLbBdGPJ3Isuk yqbtgGqvo/AMBanDVSdZICG5/GeuXneHiiibqQ2mgUR60pgTiQM2Ffm7mcCEHJnX6p30rD D64G/Oo5iJ6um4ICyQ+S6C4NGOgXzSw= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id A4B7D13A89; Thu, 1 Sep 2022 10:01:20 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id m67wJfCCEGMyXwAAMHmgww (envelope-from ); Thu, 01 Sep 2022 10:01:20 +0000 Date: Thu, 1 Sep 2022 12:01:19 +0200 From: Michal Hocko To: Marco Elver Cc: Oscar Salvador , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Vlastimil Babka , Eric Dumazet , Waiman Long , Suren Baghdasaryan , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , kasan-dev@googlegroups.com Subject: Re: [PATCH 1/3] lib/stackdepot: Add a refcount field in stack_record Message-ID: References: <20220901044249.4624-1-osalvador@suse.de> <20220901044249.4624-2-osalvador@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 01-09-22 11:18:19, Marco Elver wrote: > On Thu, 1 Sept 2022 at 10:38, Michal Hocko wrote: > > > > On Thu 01-09-22 10:24:58, Marco Elver wrote: > > > On Thu, Sep 01, 2022 at 06:42AM +0200, Oscar Salvador wrote: > > [...] > > > > diff --git a/lib/stackdepot.c b/lib/stackdepot.c > > > > index 5ca0d086ef4a..aeb59d3557e2 100644 > > > > --- a/lib/stackdepot.c > > > > +++ b/lib/stackdepot.c > > > > @@ -63,6 +63,7 @@ struct stack_record { > > > > u32 hash; /* Hash in the hastable */ > > > > u32 size; /* Number of frames in the stack */ > > > > union handle_parts handle; > > > > + refcount_t count; /* Number of the same repeated stacks */ > > > > > > This will increase stack_record size for every user, even if they don't > > > care about the count. > > > > Couldn't this be used for garbage collection? > > Only if we can precisely figure out at which point a stack is no > longer going to be needed. > > But more realistically, stack depot was designed to be simple. Right > now it can allocate new stacks (from an internal pool), but giving the > memory back to that pool isn't supported. Doing garbage collection > would effectively be a redesign of stack depot. Fair argument. > And for the purpose > for which stack depot was designed (debugging tools), memory has never > been an issue (note that stack depot also has a fixed upper bound on > memory usage). Is the increased size really a blocker then? I see how it sucks to maintain a counter when it is not used by anything but page_owner but storing that counte externally would just add more complexity AFAICS (more allocations, more tracking etc.). Maybe the counter can be conditional on the page_owner which would add some complexity as well (variable size structure) but at least the external allocation stuff could be avoided. -- Michal Hocko SUSE Labs