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 5F950C433F5 for ; Fri, 7 Jan 2022 08:55:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346227AbiAGIzM (ORCPT ); Fri, 7 Jan 2022 03:55:12 -0500 Received: from smtp-out1.suse.de ([195.135.220.28]:57262 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346229AbiAGIzK (ORCPT ); Fri, 7 Jan 2022 03:55:10 -0500 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 27E4321126; Fri, 7 Jan 2022 08:55:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1641545709; 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=rsH9bvGYmcoVLtgyOeudSiXiKCPWiynwrsli+B3sPnQ=; b=UP1E+5z3SkIzHd+AgFvtKhkj1igIXiPHVg/zKRG/6JCEPDtSsv/kAIQ8PFbHCkl0nCi/br hjj1L7x0eW/vzawzbR1Q4qKP+0Qrv/i533npRsABif8OOsXzQmjRYZWVA6IXXt2+j1B7Zd bSMWFbCfwgwfJ7VkTFpFlJvSnhKWG8E= 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 6642DA3B91; Fri, 7 Jan 2022 08:55:08 +0000 (UTC) Date: Fri, 7 Jan 2022 09:55:08 +0100 From: Michal Hocko To: Yu Zhao Cc: 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 , Vlastimil Babka , 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> 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 06-01-22 14:41:12, Yu Zhao wrote: > On Thu, Jan 06, 2022 at 05:12:16PM +0100, 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); > > > + > > > + return current->reclaim_state->mm_walk; > > > +} > > > + > > > +static void free_mm_walk(struct lru_gen_mm_walk *walk) > > > +{ > > > + if (!current->reclaim_state || !current->reclaim_state->mm_walk) > > > + kvfree(walk); > > > +} > > > > Do I get it right that you are allocating from the reclaim context? What > > prevents this to completely deplete the memory as the reclaim context is > > PF_MEMALLOC? > > Yes, and in general the same reason zram/zswap/etc. allocate memory in > the reclaim context: to make more free memory. I have to admit that I am not really familiar with zram/zswap but I find the concept of requiring memory to do the reclaim really problematic. > In this case, lru_gen_mm_walk is small (160 bytes); it's per direct > reclaimer; and direct reclaimers rarely come here, i.e., only when > kswapd can't keep up in terms of the aging, which is similar to the > condition where the inactive list is empty for the active/inactive > lru. Well, this is not a strong argument to be honest. Kswapd being stuck and the majority of the reclaim being done in the direct reclaim context is a situation I have seen many many times. We used to have problems with direct reclaimers throttling to prevent an over eager OOM situations. Have you considered using a pool of preallocated objects instead? -- Michal Hocko SUSE Labs