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Thu, 04 Aug 2022 19:44:48 -0700 (PDT) Date: Fri, 5 Aug 2022 10:44:35 +0800 From: Muchun Song To: Feng Tang Cc: Andrew Morton , Mike Kravetz , Michal Hocko , Dave Hansen , Ben Widawsky , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/hugetlb: add dedicated func to get 'allowed' nodemask for current process Message-ID: References: <20220805005903.95563-1-feng.tang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220805005903.95563-1-feng.tang@intel.com> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1659667491; a=rsa-sha256; cv=none; b=syIx98hy5F6dMsqh2k5387xtZdGHtuXsiroyXWdWyo41g9oBaajSBcw8G8yfNATYWEN6WM 4krAqZyxIReG1I/+wCumKDQVGHQuUuLQ5tg9ei+xxk6MVu6JuU51CVJvFmSOCdutm1N9Ze QZCKY7nj9AC0M+ES3zyWG9ccshYPM3U= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=EhC8cdWn; dmarc=pass (policy=none) header.from=bytedance.com; 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spf=pass (imf22.hostedemail.com: domain of songmuchun@bytedance.com designates 209.85.210.175 as permitted sender) smtp.mailfrom=songmuchun@bytedance.com X-Rspam-User: X-HE-Tag: 1659667490-933086 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Aug 05, 2022 at 08:59:03AM +0800, Feng Tang wrote: > Muchun Song found that after MPOL_PREFERRED_MANY policy was introduced > in commit b27abaccf8e8 ("mm/mempolicy: add MPOL_PREFERRED_MANY for multiple preferred nodes"), > the policy_nodemask_current()'s semantics for this new policy has been > changed, which returns 'preferred' nodes instead of 'allowed' nodes. > > With the changed semantic of policy_nodemask_current, a task with > MPOL_PREFERRED_MANY policy could fail to get its reservation even though > it can fall back to other nodes (either defined by cpusets or all online > nodes) for that reservation failing mmap calles unnecessarily early. > > The fix is to not consider MPOL_PREFERRED_MANY for reservations at all > because they, unlike MPOL_MBIND, do not pose any actual hard constrain. > > Michal suggested the policy_nodemask_current() is only used by hugetlb, > and could be moved to hugetlb code with more explicit name to enforce > the 'allowed' semantics for which only MPOL_BIND policy matters. > > apply_policy_zone() is made extern to be called in hugetlb code > and its return value is changed to bool. > > [1]. https://lore.kernel.org/lkml/20220801084207.39086-1-songmuchun@bytedance.com/t/ > > Fixes: b27abaccf8e8 ("mm/mempolicy: add MPOL_PREFERRED_MANY for multiple preferred nodes") > Reported-by: Muchun Song > Suggested-by: Michal Hocko > Signed-off-by: Feng Tang > Acked-by: Michal Hocko Thanks for fixing this. Reviewed-by: Muchun Song