linux-kernel - Re: [PATCH v8 02/14] mm/gup: check every subpage of a compound page during isolation

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Message-ID: <9f021b82-8618-3cd4-28df-1d6a9bd749cf@oracle.com>
Date:   Wed, 3 Feb 2021 16:46:32 +0000
From:   Joao Martins <joao.m.martins@...cle.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Sasha Levin <sashal@...nel.org>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        linux-kselftest@...r.kernel.org, James Morris <jmorris@...ei.org>
Subject: Re: [PATCH v8 02/14] mm/gup: check every subpage of a compound page
 during isolation

On 2/3/21 3:32 PM, Joao Martins wrote:
> On 2/3/21 2:51 PM, Pavel Tatashin wrote:
>> On Wed, Feb 3, 2021 at 8:23 AM Joao Martins <joao.m.martins@...cle.com> wrote:
>>> On 1/25/21 7:47 PM, Pavel Tatashin wrote:
>>> for compound pages but when !is_transparent_hugepage(head) or just PageHuge(head) like:
>>>
>>> +               if (!is_transparent_hugepage(head) && PageCompound(page))
>>> +                       i += (compound_nr(head) - (pages[i] - head));
>>>
>>> Or making specific to hugetlbfs:
>>>
>>> +               if (PageHuge(head))
>>> +                       i += (compound_nr(head) - (pages[i] - head));
>>
>> Yes, this is reasonable optimization. I will submit a follow up patch
>> against linux-next.

Realized it late, but the previous step was already broken. And I inherited its brokeness,
when copy-pasting the deleted chunk:

The @step should be capped at the remaining pages to iterate:

	i += min(nr_pages - i, compound_nr(head) - (pages[i] - head));

  Joao