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 3C934C4332F for ; Thu, 13 Oct 2022 11:26:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229560AbiJML0n (ORCPT ); Thu, 13 Oct 2022 07:26:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60440 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229590AbiJML0m (ORCPT ); Thu, 13 Oct 2022 07:26:42 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 208F63C8FC; Thu, 13 Oct 2022 04:26:40 -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 86F0421AEE; Thu, 13 Oct 2022 11:26:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1665660399; 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=rPzh/va1HT0bek5swCb3HGwjBRkzj98iREmCtc7/+jo=; b=kXtgnuQJJGWDKwso+qTh/xvZDwLbG3+HBKwfuMeuMVmVAKQwsJmynGOl2z4JLOiFmVLnsj M0fTKq2QnyO7yBec9P+hxdUPVXWAb5aIPMI87DERWNI551oQRlr6ZdTojLt/+LG4AyBQgn D5hQYxLDhRiIoVjWlOqFN4f5TyBjB7c= 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 5688413AAA; Thu, 13 Oct 2022 11:26:39 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id GDi/Ee/1R2OMXgAAMHmgww (envelope-from ); Thu, 13 Oct 2022 11:26:39 +0000 Date: Thu, 13 Oct 2022 13:26:38 +0200 From: Michal Hocko To: Zhongkun He Cc: corbet@lwn.net, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, wuyun.abel@bytedance.com Subject: Re: [External] Re: [RFC] mm: add new syscall pidfd_set_mempolicy() Message-ID: References: <20221010094842.4123037-1-hezhongkun.hzk@bytedance.com> <582cf257-bc0d-c96e-e72e-9164cff4fce1@bytedance.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-doc@vger.kernel.org On Thu 13-10-22 18:44:55, Zhongkun He wrote: > > On Wed 12-10-22 19:22:21, Zhongkun He wrote: > > > > > > > > Yes, this will require some refactoring and one potential way is to make > > > > mpol ref counting unconditional. The conditional ref. counting has > > > > already caused issues in the past and the code is rather hard to follow > > > > anyway. I am not really sure this optimization is worth it. > > > > > > > > Another option would be to block the pidfd side of things on completion > > > > which would wake it up from the task_work context but I would rather > > > > explore the ref counting approach first and only if this is proven to be > > > > too expensive to go with hacks like this. > > > > > > Hi Michal > > > > > > The counting approach means executing mpol_get/put() when start/finish using > > > mempolicy,right? > > > > We already do that via mpol_{get,put} but there are cases where the > > reference counting is ignored because it cannot be freed and also mpol_cond_put > > resp. open coded versions of mpol_needs_cond_ref. > > Hi Michal > > Could we try to change the MPOL_F_SHARED flag to MPOL_F_STATIC to > mark static mempolicy which cannot be freed, and mpol_needs_cond_ref > can use MPOL_F_STATIC to avoid freeing the static mempolicy. Wouldn't it make more sense to get rid of a different treatment and treat all memory policies the same way? -- Michal Hocko SUSE Labs