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 X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB920C433DB for ; Thu, 7 Jan 2021 11:17:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 988D323125 for ; Thu, 7 Jan 2021 11:17:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727360AbhAGLRd (ORCPT ); Thu, 7 Jan 2021 06:17:33 -0500 Received: from mx2.suse.de ([195.135.220.15]:49320 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726151AbhAGLRb (ORCPT ); Thu, 7 Jan 2021 06:17:31 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1610018205; 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=POfkAesmWAxZFM/w8qK4CkNJ8RSs5M/EPAXMtQXTlo0=; b=sux/5aXvVkemPDQckX+/nlpFPLNBtIrZn6aifH1txN/GKlcef9lYMVcHJhEc2xBVNQjqY6 hgewmCmUrSaX6kZKlxpWi6UAiAHZAE+3zACFevBrglj5sKPj7qi840QK9s1WBAGjzSIllg gl//9gNZp7qAVHWYQBEGTrOH5riTxXw= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id B3970AFD7; Thu, 7 Jan 2021 11:16:45 +0000 (UTC) Date: Thu, 7 Jan 2021 12:16:42 +0100 From: Michal Hocko To: Muchun Song Cc: Mike Kravetz , Andrew Morton , Naoya Horiguchi , Andi Kleen , Linux Memory Management List , LKML , Yang Shi Subject: Re: [External] Re: [PATCH v2 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one Message-ID: <20210107111642.GF13207@dhcp22.suse.cz> References: <20210106084739.63318-1-songmuchun@bytedance.com> <20210106084739.63318-2-songmuchun@bytedance.com> <20210106161327.GR13207@dhcp22.suse.cz> 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 07-01-21 10:52:21, Muchun Song wrote: > On Thu, Jan 7, 2021 at 12:13 AM Michal Hocko wrote: > > > > On Wed 06-01-21 16:47:34, Muchun Song wrote: > > > If the refcount is one when it is migrated, it means that the page > > > was freed from under us. So we are done and do not need to migrate. > > > > Is this common enough that it would warrant the explicit check for each > > migration? > > Are you worried about the overhead caused by the check? Thanks. I am not as worried as I would like to see some actual justification for this optimization. -- Michal Hocko SUSE Labs