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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: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662026482; a=rsa-sha256; cv=none; b=OndEAXNg7+DTL13ZBU9gBEqFJluTK759fX0vZYTi4EO/coOU3pLrzZN0ZF2XIOjrvvWPhC wWQhPC7ocA3J5m+Sa0pR77H+STyWo3k4a0pkOGLEJjYCSN7cFaKlJcfSgJbxVNIewfzueS qSmDFkcHnXXKwAzAJrGNbcKktfutqRQ= ARC-Authentication-Results: i=1; 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dmarc=pass (policy=quarantine) header.from=suse.com X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 0C1811C0047 X-Stat-Signature: f7pahi97khqztfo64n9ehr76sqi43umq X-HE-Tag: 1662026481-864343 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 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