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 E3968C433FE for ; Mon, 10 Jan 2022 16:25:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237327AbiAJQZT (ORCPT ); Mon, 10 Jan 2022 11:25:19 -0500 Received: from smtp-out2.suse.de ([195.135.220.29]:52850 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237311AbiAJQZS (ORCPT ); Mon, 10 Jan 2022 11:25:18 -0500 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id C262C1F393; Mon, 10 Jan 2022 16:25:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1641831916; 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=Y7C3iBFO6mPZG0zqznbI9unOua16tjFDplhQ2oT/yec=; b=DQBwKbxwJZEyQg10FCROT+HMkMX/2RAAibSv0z8ACXSJtgY9OdtKzOSdJIOVMoHvfJqI9X /RlcxZJdjiCsps9h11Hji2qnDEXcFPStpt9VuWTgk2zXTUvh8rh6hZ33fEfBJ5kBXTPzBo 377kRe33OmnPdldc821hy8euxse9hpM= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id EDB44A3B88; Mon, 10 Jan 2022 16:25:15 +0000 (UTC) Date: Mon, 10 Jan 2022 17:25:15 +0100 From: Michal Hocko To: Vlastimil Babka Cc: Yu Zhao , Andrew Morton , Linus Torvalds , Andi Kleen , Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Jesse Barnes , Johannes Weiner , Jonathan Corbet , Matthew Wilcox , Mel Gorman , Michael Larabel , Rik van Riel , Will Deacon , Ying Huang , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, page-reclaim@google.com, x86@kernel.org, Konstantin Kharlamov Subject: Re: [PATCH v6 6/9] mm: multigenerational lru: aging Message-ID: References: <20220104202227.2903605-1-yuzhao@google.com> <20220104202227.2903605-7-yuzhao@google.com> <8edfd643-888b-fbe6-97c0-21f900767c27@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8edfd643-888b-fbe6-97c0-21f900767c27@suse.cz> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 10-01-22 17:01:07, Vlastimil Babka wrote: > On 1/10/22 16:01, Michal Hocko wrote: > > On Thu 06-01-22 17:12:18, Michal Hocko wrote: > >> On Tue 04-01-22 13:22:25, Yu Zhao wrote: > >> > +static struct lru_gen_mm_walk *alloc_mm_walk(void) > >> > +{ > >> > + if (!current->reclaim_state || !current->reclaim_state->mm_walk) > >> > + return kvzalloc(sizeof(struct lru_gen_mm_walk), GFP_KERNEL); > > > > One thing I have overlooked completely. You cannot really use GFP_KERNEL > > allocation here because the reclaim context can be constrained (e.g. > > GFP_NOFS). This allocation will not do any reclaim as it is PF_MEMALLOC > > but I suspect that the lockdep will complain anyway. > > > > Also kvmalloc is not really great here. a) vmalloc path is never > > executed for small objects and b) we do not really want to make a > > dependency between vmalloc and the reclaim (by vmalloc -> reclaim -> > > vmalloc). > > > > Even if we rule out vmalloc and look at kmalloc alone. Is this really > > safe? I do not see any recursion prevention in the SL.B code. Maybe this > > just happens to work but the dependency should be really documented so > > that future SL.B changes won't break the whole scheme. > > Slab implementations drop all locks before calling into page allocator (thus > possibly reclaim) so slab itself should be fine and I don't expect it to > change. But we could eventually reach the page allocator recursively again, > that's true and not great. Thanks for double checking. If recursion is really intended and something SL.B allocators should support then this is definitely worth documenting so that a subtle change won't break in the future. -- Michal Hocko SUSE Labs