From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yang Shi Subject: Re: [v2 PATCH 2/2] mm: mempolicy: handle vma with unmovable pages mapped correctly in mbind Date: Wed, 17 Jul 2019 12:25:07 -0700 Message-ID: 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> <7be3d36a-19fe-2e3b-8840-27fb5fd60f15@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <7be3d36a-19fe-2e3b-8840-27fb5fd60f15@suse.cz> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Vlastimil Babka , mhocko@kernel.org, mgorman@techsingularity.net, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Linux API List-Id: linux-api@vger.kernel.org On 7/17/19 11:50 AM, Vlastimil Babka wrote: > 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? Yes, I agree the man page does looks ambiguous.  Anyway, I think we could add a patch later to kernel or manpage for either interpretations once it gets clarified. > >> 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, >>>>>