linux-kernel - Re: [PATCH 0/3] mm/hugetlb: hugepage migration enhancements

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Date:   Fri, 23 Sep 2022 15:51:25 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Doug Berger <opendmb@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Muchun Song <songmuchun@...edance.com>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Florian Fainelli <f.fainelli@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] mm/hugetlb: hugepage migration enhancements

On 09/22/22 16:27, Doug Berger wrote:
> On 9/22/2022 3:41 PM, Mike Kravetz wrote:
> > On 09/22/22 13:25, Mike Kravetz wrote:
> > > On 09/21/22 15:36, Doug Berger wrote:
> > > 
> > > As noted above, for pages to be migrated we first try to use an existing
> > > free huge page as the target.  Quite some time ago, Michal added code to
> > > allocate a new page from buddy as the target if no free huge pages were
> > > available.  This change also included a special flag to dissolve the
> > > source huge page when it is freed.  It seems like this is the exact
> > > behavior we want here?  I wonder if it might be easier just to use this
> > > existing code?
> > 
> > Totally untested, but I believe the patch below would accomplish this.
> > 
> >  From aa8fc11bb67bc9e67e3b6b280fab339afce37759 Mon Sep 17 00:00:00 2001
> > From: Mike Kravetz <mike.kravetz@...cle.com>
> > Date: Thu, 22 Sep 2022 15:32:10 -0700
> > Subject: [PATCH] hugetlb: force alloc_contig_range hugetlb migrations to
> >   allocate new pages
> > 
> > When migrating hugetlb pages as the result of an alloc_contig_range
> > operation, allocate a new page from buddy for the migration target.
> > This guarantees that the number of hugetlb pages is not decreased by
> > the operation.  In addition, this will result in the special HPageTemporary
> > flag being set in the source page so that it will be dissolved when
> > freed.
> > 
<snip>
> I believe I exposed alloc_migrate_huge_page() and conditionally invoked it
> from alloc_migration_target() when in alloc_contig, which is roughly
> equivalent. I didn't consider modifying the mtc to pass the information so
> my logic in alloc_migration_target() was a little kludgy.
> 
> Like I said, this can be made to work and I'm happy to accept an alternative
> if others agree. I think the isolation test of patch 3 is also still
> desirable.

Yes, hoping to get some other opinions as well.

I do agree that patch 3 is still a good idea.
-- 
Mike Kravetz