From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
akpm@linux-foundation.org, Michal Hocko <mhocko@kernel.org>,
mpe@ellerman.id.au, paulus@samba.org,
David Gibson <david@gibson.dropbear.id.au>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH V5 1/3] mm: Add get_user_pages_cma_migrate
Date: Thu, 20 Dec 2018 16:48:30 +1100 [thread overview]
Message-ID: <23cae5a6-4370-224c-523c-ab6ee940cf87@ozlabs.ru> (raw)
In-Reply-To: <b316eb1c-36dc-49e0-f46f-e610f29b6058@linux.ibm.com>
On 20/12/2018 16:22, Aneesh Kumar K.V wrote:
> On 12/20/18 9:49 AM, Alexey Kardashevskiy wrote:
>>
>>
>> On 19/12/2018 14:40, Aneesh Kumar K.V wrote:
>>> This helper does a get_user_pages_fast and if it find pages in the
>>> CMA area
>>> it will try to migrate them before taking page reference. This makes
>>> sure that
>>> we don't keep non-movable pages (due to page reference count) in the
>>> CMA area.
>>> Not able to move pages out of CMA area result in CMA allocation
>>> failures.
>>>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>
>
> .....
>>> + * We did migrate all the pages, Try to get the page
>>> references again
>>> + * migrating any new CMA pages which we failed to isolate
>>> earlier.
>>> + */
>>> + drain_allow = true;
>>> + goto get_user_again;
>>
>>
>> So it is possible to have pages pinned, then successfully migrated
>> (migrate_pages() returned 0), then pinned again, then some pages may end
>> up in CMA again and migrate again and nothing seems to prevent this loop
>> from being endless. What do I miss?
>>
>
> pages used as target page for migration won't be allocated from CMA region.
Then migrate_allow should be set to "false" regardless what
migrate_pages() returned and then I am totally missing the point of this
goto and going through the loop again even when we know for sure it
won't do literally anything but checking is_migrate_cma_page() even
though we know pages won't be allocated from CMA.
It should be simple gup_fast() instead of goto and then we won't need
goto/migrate_allow.
--
Alexey
WARNING: multiple messages have this Message-ID (diff)
From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
akpm@linux-foundation.org, Michal Hocko <mhocko@kernel.org>,
mpe@ellerman.id.au, paulus@samba.org,
David Gibson <david@gibson.dropbear.id.au>
Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH V5 1/3] mm: Add get_user_pages_cma_migrate
Date: Thu, 20 Dec 2018 16:48:30 +1100 [thread overview]
Message-ID: <23cae5a6-4370-224c-523c-ab6ee940cf87@ozlabs.ru> (raw)
In-Reply-To: <b316eb1c-36dc-49e0-f46f-e610f29b6058@linux.ibm.com>
On 20/12/2018 16:22, Aneesh Kumar K.V wrote:
> On 12/20/18 9:49 AM, Alexey Kardashevskiy wrote:
>>
>>
>> On 19/12/2018 14:40, Aneesh Kumar K.V wrote:
>>> This helper does a get_user_pages_fast and if it find pages in the
>>> CMA area
>>> it will try to migrate them before taking page reference. This makes
>>> sure that
>>> we don't keep non-movable pages (due to page reference count) in the
>>> CMA area.
>>> Not able to move pages out of CMA area result in CMA allocation
>>> failures.
>>>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>
>
> .....
>>> + * We did migrate all the pages, Try to get the page
>>> references again
>>> + * migrating any new CMA pages which we failed to isolate
>>> earlier.
>>> + */
>>> + drain_allow = true;
>>> + goto get_user_again;
>>
>>
>> So it is possible to have pages pinned, then successfully migrated
>> (migrate_pages() returned 0), then pinned again, then some pages may end
>> up in CMA again and migrate again and nothing seems to prevent this loop
>> from being endless. What do I miss?
>>
>
> pages used as target page for migration won't be allocated from CMA region.
Then migrate_allow should be set to "false" regardless what
migrate_pages() returned and then I am totally missing the point of this
goto and going through the loop again even when we know for sure it
won't do literally anything but checking is_migrate_cma_page() even
though we know pages won't be allocated from CMA.
It should be simple gup_fast() instead of goto and then we won't need
goto/migrate_allow.
--
Alexey
next prev parent reply other threads:[~2018-12-20 5:49 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-19 3:40 [PATCH V5 0/3] mm/kvm/vfio/ppc64: Migrate compound pages out of CMA region Aneesh Kumar K.V
2018-12-19 3:40 ` Aneesh Kumar K.V
2018-12-19 3:40 ` [PATCH V5 1/3] mm: Add get_user_pages_cma_migrate Aneesh Kumar K.V
2018-12-19 3:40 ` Aneesh Kumar K.V
2018-12-20 4:19 ` Alexey Kardashevskiy
2018-12-20 4:19 ` Alexey Kardashevskiy
2018-12-20 5:22 ` Aneesh Kumar K.V
2018-12-20 5:22 ` Aneesh Kumar K.V
2018-12-20 5:48 ` Alexey Kardashevskiy [this message]
2018-12-20 5:48 ` Alexey Kardashevskiy
2018-12-20 5:52 ` Aneesh Kumar K.V
2018-12-20 5:52 ` Aneesh Kumar K.V
2018-12-20 6:20 ` Alexey Kardashevskiy
2018-12-20 6:20 ` Alexey Kardashevskiy
2018-12-20 6:26 ` Aneesh Kumar K.V
2018-12-20 6:26 ` Aneesh Kumar K.V
2018-12-20 4:28 ` Alexey Kardashevskiy
2018-12-20 4:28 ` Alexey Kardashevskiy
2018-12-19 3:40 ` [PATCH V5 2/3] powerpc/mm/iommu: Allow migration of cma allocated pages during mm_iommu_get Aneesh Kumar K.V
2018-12-19 3:40 ` Aneesh Kumar K.V
2018-12-20 5:16 ` Alexey Kardashevskiy
2018-12-20 5:16 ` Alexey Kardashevskiy
2018-12-19 3:40 ` [PATCH V5 3/3] powerpc/mm/iommu: Allow large IOMMU page size only for hugetlb backing Aneesh Kumar K.V
2018-12-19 3:40 ` Aneesh Kumar K.V
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=23cae5a6-4370-224c-523c-ab6ee940cf87@ozlabs.ru \
--to=aik@ozlabs.ru \
--cc=akpm@linux-foundation.org \
--cc=aneesh.kumar@linux.ibm.com \
--cc=david@gibson.dropbear.id.au \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mhocko@kernel.org \
--cc=mpe@ellerman.id.au \
--cc=paulus@samba.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.