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 38D3EECAAA1 for ; Tue, 6 Sep 2022 03:55:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238015AbiIFDzd (ORCPT ); Mon, 5 Sep 2022 23:55:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56652 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233083AbiIFDzG (ORCPT ); Mon, 5 Sep 2022 23:55:06 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A3C131403D for ; Mon, 5 Sep 2022 20:54:55 -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-out2.suse.de (Postfix) with ESMTPS id EA0E21F8F5; Tue, 6 Sep 2022 03:54:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1662436493; 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=wSRahjjgGZuy7SAGmGAziVDOy+dePLJGxm+nbGz1xQs=; b=0r2him/7A7lO2AaP2zJRSEqXLj6qDVz+jhQSLrH9rWMFZYjB1GBsYe6CcP5EeJjGVd6QpG TV1dbupG79lcAAnW1hxQtuvqJESwvesnHunQuwjWDbDDkMEQhUSRkDHsOeojFudnDAR3oP QGfciLYON15UP7iv82WKX2i/gzvdUyE= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1662436493; 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=wSRahjjgGZuy7SAGmGAziVDOy+dePLJGxm+nbGz1xQs=; b=Jv/sE0gzGBvf5gnCz0Nvl9mSkO7T5doUVrR4k8V+4vkyjyqiKr8fzDb1FsLmg6z+wSTLRh cgvwFDF7Bgv2JUBQ== 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 5798B13A19; Tue, 6 Sep 2022 03:54:53 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id ho7ZEo3EFmNWbwAAMHmgww (envelope-from ); Tue, 06 Sep 2022 03:54:53 +0000 Date: Tue, 6 Sep 2022 05:54:51 +0200 From: Oscar Salvador To: Andrey Konovalov Cc: Andrew Morton , LKML , Linux Memory Management List , Michal Hocko , Vlastimil Babka , Eric Dumazet , Waiman Long , Suren Baghdasaryan , Marco Elver , Alexander Potapenko Subject: Re: [PATCH v2 1/3] lib/stackdepot: Add a refcount field in stack_record Message-ID: References: <20220905031012.4450-1-osalvador@suse.de> <20220905031012.4450-2-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 Mon, Sep 05, 2022 at 10:57:20PM +0200, Andrey Konovalov wrote: > On Mon, Sep 5, 2022 at 5:10 AM Oscar Salvador wrote: > > +enum stack_depot_action { > > + STACK_DEPOT_ACTION_NONE, > > + STACK_DEPOT_ACTION_COUNT, > > +}; > > Hi Oscar, Hi Andrey > Why do we need these actions? Why not just increment the refcount on > each stack trace save? Let me try to explain it. Back in RFC, there were no actions and the refcount was incremented/decremented in __set_page_ownwer() and __reset_page_owner() functions. This lead to a performance "problem", where you would look for the stack twice, one when save it and one when increment it. We figured we could do better and, at least, for the __set_page_owner() we could look just once for the stacktrace when calling __stack_depot_save, and increment it directly there. We cannot do that for __reset_page_owner(), because the stack we are saving is the freeing stacktrace, and we are not interested in that. That is why __reset_page_owner() does: <--- depot_stack_handle_t alloc_handle; ... alloc_handle = page_owner->handle; handle = save_stack(GFP_NOWAIT | __GFP_NOWARN, STACK_DEPOT_ACTION_NONE); page_owner->free_handle = handle stack_depot_dec_count(alloc_handle); ---> alloc_handle contains the handle for the allocation stacktrace, which was set in __set_page_owner(), and page_owner->free handle contains the handle for the freeing stacktrace. But we are only interested in the allocation stack and we only want to increment/decrement that on allocation/free. > Could you split out the stack depot and the page_owner changes into > separate patches? I could, I am not sure if it would make the review any easier though, as you could not match stackdepot <-> page_owner changes. And we should be adding a bunch of code that would not be used till later on. But I can try it out if there is a strong opinion. thanks for your time! -- Oscar Salvador SUSE Labs