From: Oscar Salvador <osalvador@suse.de>
To: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
David Hildenbrand <david@redhat.com>,
Muchun Song <songmuchun@bytedance.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] mm: Make alloc_contig_range handle free hugetlb pages
Date: Thu, 18 Feb 2021 11:09:17 +0100 [thread overview]
Message-ID: <20210218100917.GA4842@localhost.localdomain> (raw)
In-Reply-To: <YC0ve4PP+VTrEEtw@dhcp22.suse.cz>
On Wed, Feb 17, 2021 at 04:00:11PM +0100, Michal Hocko wrote:
> Is this really necessary? dissolve_free_huge_page will take care of this
> and the race windown you are covering is really tiny.
Probably not, I was trying to shrink to race window as much as possible
but the call to dissolve_free_huge_page might be enough.
> > + nid = page_to_nid(page);
> > + spin_unlock(&hugetlb_lock);
> > +
> > + /*
> > + * Before dissolving the page, we need to allocate a new one,
> > + * so the pool remains stable.
> > + */
> > + new_page = alloc_fresh_huge_page(h, gfp_mask, nid, nmask, NULL);
>
> wrt. fallback to other zones, I haven't realized that the primary
> usecase is a form of memory offlining (from virt-mem). I am not yet sure
> what the proper behavior is in that case but if breaking hugetlb pools,
> similar to the normal hotplug operation, is viable then this needs a
> special mode. We do not want a random alloc_contig_range user to do the
> same. So for starter I would go with __GFP_THISNODE here.
Ok, makes sense.
__GFP_THISNODE will not allow fallback to other node's zones.
Since we only allow the nid the page belongs to, nodemask should be
NULL, right?
> > + if (!h)
> > + /*
> > + * The page might have been dissolved from under our feet.
> > + * If that is the case, return success as if we dissolved it
> > + * ourselves.
> > + */
> > + return true;
>
> nit I would put the comment above the conditin for both cases. It reads
> more easily that way. At least without { }.
Yes, makes sense.
> Other than that I haven't noticed any surprises.
I did. The 'put_page' call should be placed above, right after getting
the page. Otherwise, refcount == 1 and we will fail to dissolve the
new page if we need to (in case old page fails to be dissolved).
I already fixed that locally.
--
Oscar Salvador
SUSE L3
next prev parent reply other threads:[~2021-02-18 10:09 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-17 10:08 [PATCH 0/2] Make alloc_contig_range handle Hugetlb pages Oscar Salvador
2021-02-17 10:08 ` [PATCH 1/2] mm: Make alloc_contig_range handle free hugetlb pages Oscar Salvador
2021-02-17 13:30 ` Michal Hocko
2021-02-17 13:36 ` David Hildenbrand
2021-02-17 13:50 ` Michal Hocko
2021-02-17 13:53 ` David Hildenbrand
2021-02-17 13:59 ` Michal Hocko
2021-02-17 14:08 ` David Hildenbrand
2021-02-17 14:14 ` Michal Hocko
2021-02-17 14:23 ` Oscar Salvador
2021-02-17 13:42 ` Oscar Salvador
2021-02-17 15:00 ` Michal Hocko
2021-02-18 10:09 ` Oscar Salvador [this message]
2021-02-18 12:52 ` Michal Hocko
2021-02-18 13:32 ` Oscar Salvador
2021-02-18 13:59 ` Michal Hocko
2021-02-18 16:53 ` Oscar Salvador
2021-02-19 9:05 ` Oscar Salvador
2021-02-19 9:56 ` Michal Hocko
2021-02-19 10:14 ` Oscar Salvador
2021-02-19 20:00 ` Mike Kravetz
2021-02-19 10:40 ` Oscar Salvador
2021-02-19 10:55 ` Michal Hocko
2021-02-19 11:17 ` Oscar Salvador
2021-02-19 11:24 ` Michal Hocko
2021-02-17 10:08 ` [PATCH 2/2] mm: Make alloc_contig_range handle in-use " Oscar Salvador
2021-02-17 13:36 ` Michal Hocko
2021-02-17 13:46 ` Oscar Salvador
2021-02-17 13:54 ` Michal Hocko
2021-02-17 15:06 ` Michal Hocko
2021-02-17 15:27 ` Oscar Salvador
2021-02-17 15:33 ` Michal Hocko
2021-02-18 6:01 ` Oscar Salvador
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