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[195.135.220.15]) by mx.google.com with ESMTPS id gq12si13668690ejb.170.2019.07.17.11.50.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Jul 2019 11:50:07 -0700 (PDT) Received-SPF: pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 6A023AC10; Wed, 17 Jul 2019 18:50:07 +0000 (UTC) Subject: Re: [v2 PATCH 2/2] mm: mempolicy: handle vma with unmovable pages mapped correctly in mbind To: Yang Shi , mhocko@kernel.org, mgorman@techsingularity.net, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Linux API References: <1561162809-59140-1-git-send-email-yang.shi@linux.alibaba.com> <1561162809-59140-3-git-send-email-yang.shi@linux.alibaba.com> <0cbc99f6-76a9-7357-efa7-a2d551b3cd12@suse.cz> <9defdc16-c825-05b7-b394-abdf39000220@linux.alibaba.com> <3197a7df-c7bc-2bac-3d40-dbfc97d4a909@linux.alibaba.com> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <3197a7df-c7bc-2bac-3d40-dbfc97d4a909@linux.alibaba.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit 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 7/17/19 8:23 PM, Yang Shi wrote: > > > On 7/16/19 10:28 AM, Yang Shi wrote: >> >> >> On 7/16/19 5:07 AM, Vlastimil Babka wrote: >>> On 6/22/19 2:20 AM, Yang Shi wrote: >>>> @@ -969,10 +975,21 @@ static long do_get_mempolicy(int *policy, >>>> nodemask_t *nmask, >>>>   /* >>>>    * page migration, thp tail pages can be passed. >>>>    */ >>>> -static void migrate_page_add(struct page *page, struct list_head >>>> *pagelist, >>>> +static int migrate_page_add(struct page *page, struct list_head >>>> *pagelist, >>>>                   unsigned long flags) >>>>   { >>>>       struct page *head = compound_head(page); >>>> + >>>> +    /* >>>> +     * Non-movable page may reach here.  And, there may be >>>> +     * temporaty off LRU pages or non-LRU movable pages. >>>> +     * Treat them as unmovable pages since they can't be >>>> +     * isolated, so they can't be moved at the moment.  It >>>> +     * should return -EIO for this case too. >>>> +     */ >>>> +    if (!PageLRU(head) && (flags & MPOL_MF_STRICT)) >>>> +        return -EIO; >>>> + >>> Hm but !PageLRU() is not the only way why queueing for migration can >>> fail, as can be seen from the rest of the function. Shouldn't all cases >>> be reported? >> >> Do you mean the shared pages and isolation failed pages? I'm not sure >> whether we should consider these cases break the semantics or not, so >> I leave them as they are. But, strictly speaking they should be >> reported too, at least for the isolation failed page. CC'd linux-api, should be done on v3 posting also. > By reading mbind man page, it says: > > If MPOL_MF_MOVE is specified in flags, then the kernel will attempt to > move all the existing pages in the memory range so that they follow the > policy.  Pages that are shared with other processes will not be moved.  > If MPOL_MF_STRICT is also specified, then the call fails with the error > EIO if some pages could not be moved. I don't think this means that for shared pages, -EIO should not be reported. I can imagine both interpretations of the paragraph. I guess we can be conservative and keep not reporting them, if that was always the case - but then perhaps clarify the man page? > It looks the code already handles shared page correctly, we just need > return -EIO for isolation failed page if MPOL_MF_STRICT is specified. > >> >> Thanks, >> Yang >> >>> >>>>       /* >>>>        * Avoid migrating a page that is shared with others. >>>>        */ >>>> @@ -984,6 +1001,8 @@ static void migrate_page_add(struct page *page, >>>> struct list_head *pagelist, >>>>                   hpage_nr_pages(head)); >>>>           } >>>>       } >>>> + >>>> +    return 0; >>>>   } >>>>     /* page allocation callback for NUMA node migration */ >>>> @@ -1186,9 +1205,10 @@ static struct page *new_page(struct page >>>> *page, unsigned long start) >>>>   } >>>>   #else >>>>   -static void migrate_page_add(struct page *page, struct list_head >>>> *pagelist, >>>> +static int migrate_page_add(struct page *page, struct list_head >>>> *pagelist, >>>>                   unsigned long flags) >>>>   { >>>> +    return -EIO; >>>>   } >>>>     int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from, >>>> >> >