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

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On Thu 28-01-21 14:15:31, Andrew Morton wrote:
> On Thu, 28 Jan 2021 14:00:29 -0800 Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
> 
> > On 1/28/21 1:37 PM, Andrew Morton wrote:
> > > On Thu, 28 Jan 2021 06:52:21 +0100 Oscar Salvador <osalvador@xxxxxxx> 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.
> 
> I guess just one patch is best for reviewers.  Then I'll split up into
> a sprinkle of -fix patches if I'm feeling energetic ;)

A single patch on top should be just fine. It is not like this would be
a bisectability breaker.

-- 
Michal Hocko
SUSE Labs




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