From: Joao Martins <joao.m.martins@oracle.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, vbabka@suse.cz, mhocko@suse.com,
david@redhat.com, osalvador@suse.de, dan.j.williams@intel.com,
sashal@kernel.org, tyhicks@linux.microsoft.com,
iamjoonsoo.kim@lge.com, mike.kravetz@oracle.com,
rostedt@goodmis.org, mingo@redhat.com, peterz@infradead.org,
mgorman@suse.de, willy@infradead.org, rientjes@google.com,
jhubbard@nvidia.com, linux-doc@vger.kernel.org,
ira.weiny@intel.com, linux-kselftest@vger.kernel.org,
jmorris@namei.org
Subject: Re: [PATCH v8 02/14] mm/gup: check every subpage of a compound page during isolation
Date: Wed, 3 Feb 2021 16:13:21 +0000 [thread overview]
Message-ID: <f82dca38-52bd-aa27-2d27-b5a67f5284f5@oracle.com> (raw)
In-Reply-To: <20210203145313.GQ4718@ziepe.ca>
On 2/3/21 2:53 PM, Jason Gunthorpe wrote:
> On Wed, Feb 03, 2021 at 01:22:18PM +0000, Joao Martins wrote:
>
>> With this, longterm gup will 'regress' for hugetlbfs e.g. from ~6k -> ~32k usecs when
>> pinning a 16G hugetlb file.
>
> Yes, but correctness demands it.
>
Hence the quotes around the word regress.
But still, we are adding unnecessary overhead (previously nonexistent) to compound pages
even those where the issue doesn't exist (hugetlb).
> The solution is to track these pages as we discover them so we know if
> a PMD/PUD points and can directly skip the duplicated work
>
That looks better. It would require moving check_and_migrate_movable_pages() elsewhere,
and/or possibly reworking the entire series?
>> Splitting can only occur on THP right? If so, perhaps we could
>> retain the @step increment for compound pages but when
>> !is_transparent_hugepage(head) or just PageHuge(head) like:
>
> Honestly I'd rather see it fixed properly which will give even bigger
> performance gains - avoiding the entire rescan of the page list will
> be a win
>
If check_and_migrate_movable_pages() is meant to migrate unpinned pages, then rather than
pinning+unpinning+moving, perhaps it would be called in __get_user_pages() place where we
are walking page tables and know if it's a PUD/PMD and can skip all the subpages and just
record and migrate those instead. Was that your thinking?
Joao
next prev parent reply other threads:[~2021-02-03 16:15 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 19:47 [PATCH v8 00/14] prohibit pinning pages in ZONE_MOVABLE Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 01/14] mm/gup: don't pin migrated cma pages in movable zone Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 02/14] mm/gup: check every subpage of a compound page during isolation Pavel Tatashin
2021-02-03 13:22 ` Joao Martins
2021-02-03 14:51 ` Pavel Tatashin
2021-02-03 14:51 ` Pavel Tatashin
2021-02-03 15:32 ` Joao Martins
2021-02-03 16:46 ` Joao Martins
2021-02-03 14:53 ` Jason Gunthorpe
2021-02-03 16:13 ` Joao Martins [this message]
2021-02-03 18:00 ` Jason Gunthorpe
2021-01-25 19:47 ` [PATCH v8 03/14] mm/gup: return an error on migration failure Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 04/14] mm/gup: check for isolation errors Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 05/14] mm cma: rename PF_MEMALLOC_NOCMA to PF_MEMALLOC_PIN Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 06/14] mm: apply per-task gfp constraints in fast path Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 07/14] mm: honor PF_MEMALLOC_PIN for all movable pages Pavel Tatashin
[not found] ` <20210131130903.4875-1-lecopzer@gmail.com>
2021-01-31 16:03 ` Pavel Tatashin
2021-01-31 16:03 ` Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 08/14] mm/gup: do not migrate zero page Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 09/14] mm/gup: migrate pinned pages out of movable zone Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 10/14] memory-hotplug.rst: add a note about ZONE_MOVABLE and page pinning Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 11/14] mm/gup: change index type to long as it counts pages Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 12/14] mm/gup: longterm pin migration cleanup Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 13/14] selftests/vm: gup_test: fix test flag Pavel Tatashin
2021-01-25 19:47 ` [PATCH v8 14/14] selftests/vm: gup_test: test faulting in kernel, and verify pinnable pages Pavel Tatashin
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