linux-kernel - Re: [PATCH v3 3/5] hugetlb: only set HPageMigratable for migratable hstates

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Message-ID: <12187293-e972-acd8-7789-22ebfa736f95@oracle.com>
Date:   Thu, 28 Jan 2021 14:00:29 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>
Cc:     Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Muchun Song <songmuchun@...edance.com>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Miaohe Lin <linmiaohe@...wei.com>
Subject: Re: [PATCH v3 3/5] hugetlb: only set HPageMigratable for migratable
 hstates

On 1/28/21 1:37 PM, Andrew Morton wrote:
> On Thu, 28 Jan 2021 06:52:21 +0100 Oscar Salvador <osalvador@...e.de> wrote:
> 
>> On Wed, Jan 27, 2021 at 03:36:41PM -0800, Mike Kravetz wrote:
>>> Yes, this patch is somewhat optional.  It should be a minor improvement
>>> in cases where we are dealing with hpages in a non-migratable hstate.
>>> Although, I do not believe this is the common case.
>>>
>>> The real reason for even looking into this was a comment by Oscar.  With
>>> the name change to HPageMigratable, it implies that the page is migratable.
>>> However, this is not the case if the page's hstate does not support migration.
>>> So, if we check the hstate when setting the flag we can eliminate those
>>> cases where the page is certainly not migratable.
>>>
>>> I don't really love this patch.  It has minimal functional value.
>>>
>>> Oscar, what do you think about dropping this?
>>
>> Yeah, I remember this topic arose during a discussion of patch#2 in the
>> early versions, about whether the renaming to HPageMigratable made
>> sense.
>>
>> Back then I thought that we could have this in one place at fault-path [1],
>> which should have made this prettier, but it is not the case.
>> True is that the optimization is little, so I am fine with dropping this
>> patch.
> 
> I've dropped it.

Thanks Andrew.

Michal suggested that comments describing synchronization be added for each
flag.  Since I did 'one patch per flag', that would be an update to each patch.
Or, I could simply add a patch to update the comment block based on what you
already have.

Let me know what is best/easiest for you.
-- 
Mike Kravetz