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

[Oscar Salvador]

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.

unmap_and_move_huge_page() fences off pages belonging to non-migratable
hstates.

[1] https://patchwork.kernel.org/project/linux-mm/patch/20210120013049.311822-3-mike.kravetz@xxxxxxxxxx/#23914033

Thanks

-- 
Oscar Salvador
SUSE L3