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From: Vlastimil Babka <email@example.com>
To: Mike Kravetz <firstname.lastname@example.org>,
Cc: Reinette Chatre <email@example.com>,
Michal Hocko <firstname.lastname@example.org>,
Christopher Lameter <email@example.com>,
Guy Shattah <firstname.lastname@example.org>,
Anshuman Khandual <email@example.com>,
Michal Nazarewicz <firstname.lastname@example.org>,
David Nellans <email@example.com>,
Laura Abbott <firstname.lastname@example.org>, Pavel Machek <email@example.com>,
Dave Hansen <firstname.lastname@example.org>,
Andrew Morton <email@example.com>,
Joonsoo Kim <firstname.lastname@example.org>
Subject: Re: [PATCH v2 2/4] mm: check for proper migrate type during isolation
Date: Tue, 22 May 2018 09:07:56 +0200 [thread overview]
Message-ID: <email@example.com> (raw)
On 05/22/2018 01:10 AM, Mike Kravetz wrote:
> On 05/18/2018 03:32 AM, Vlastimil Babka wrote:
>> On 05/04/2018 01:29 AM, Mike Kravetz wrote:
>>> The routine start_isolate_page_range and alloc_contig_range have
>>> comments saying that migratetype must be either MIGRATE_MOVABLE or
>>> MIGRATE_CMA. However, this is not enforced.
>> Enforced, no. But if the pageblocks really were as such, it used to
>> shortcut has_unmovable_pages(). This was wrong and removed in
>> d7b236e10ced ("mm: drop migrate type checks from has_unmovable_pages")
>> plus 4da2ce250f98 ("mm: distinguish CMA and MOVABLE isolation in
>> What is important is
>>> that that all pageblocks in the range are of type migratetype.
>> the same
>>> This is because blocks will be set to migratetype on error.
>> Strictly speaking this is true only for the CMA case. For other cases,
>> the best thing actually would be to employ the same heuristics as page
>> allocation migratetype fallbacks, and count how many pages are free and
>> how many appear to be movable, see how steal_suitable_fallback() uses
>> the last parameter of move_freepages_block().
>>> Add a boolean argument enforce_migratetype to the routine
>>> start_isolate_page_range. If set, it will check that all pageblocks
>>> in the range have the passed migratetype. Return -EINVAL is pageblock
>>> is wrong type is found in range.
>>> A boolean is used for enforce_migratetype as there are two primary
>>> users. Contiguous range allocation which wants to enforce migration
>>> type checking. Memory offline (hotplug) which is not concerned about
>>> type checking.
>> This is missing some high-level result. The end change is that CMA is
>> now enforcing. So we are making it more robust when it's called on
>> non-CMA pageblocks by mistake? (BTW I still do hope we can remove
>> MIGRATE_CMA soon after Joonsoo's ZONE_MOVABLE CMA conversion. Combined
>> with my suggestion above we could hopefully get rid of the migratetype
>> parameter completely instead of enforcing it?). Is this also a
>> preparation for introducing find_alloc_contig_pages() which will be
>> enforcing? (I guess, and will find out shortly, but it should be stated
> Thank you for looking at these patches Vlastimil.
> My primary motivation for this patch was the 'error recovery' in
> start_isolate_page_range. It takes a range and attempts to set
> all pageblocks to MIGRATE_ISOLATE. If it encounters an error after
> setting some blocks to isolate, it will 'clean up' by setting the
> migrate type of previously modified blocks to the passed migratetype.
> So, one possible side effect of an error in start_isolate_page_range
> is that the migrate type of some pageblocks could be modified. Thinking
> about it more now, that may be OK.
It would be definitely OK if the migratetype was changed similarly as
steal_suitable_fallback() does it, as I've said above.
> It just does not seem like the
> right thing to do, especially with comments saying "migratetype must
> be either MIGRATE_MOVABLE or MIGRATE_CMA". I'm fine with leaving the
> code as is and just cleaning up the comments if you think that may
> be better.
That's also possible, especially when the code is restructured as I've
suggested in the other reply, which should significantly reduce the
amount of error recoveries.
next prev parent reply other threads:[~2018-05-22 7:08 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-03 23:29 [PATCH v2 0/4] Interface for higher order contiguous allocations Mike Kravetz
2018-05-03 23:29 ` [PATCH v2 1/4] mm: change type of free_contig_range(nr_pages) to unsigned long Mike Kravetz
2018-05-18 9:12 ` Vlastimil Babka
2018-05-18 22:01 ` Mike Kravetz
2018-05-03 23:29 ` [PATCH v2 2/4] mm: check for proper migrate type during isolation Mike Kravetz
2018-05-18 10:32 ` Vlastimil Babka
2018-05-21 23:10 ` Mike Kravetz
2018-05-22 7:07 ` Vlastimil Babka [this message]
2018-05-03 23:29 ` [PATCH v2 3/4] mm: add find_alloc_contig_pages() interface Mike Kravetz
2018-05-21 8:54 ` Vlastimil Babka
2018-05-21 23:48 ` Mike Kravetz
2018-05-22 16:41 ` Reinette Chatre
2018-05-22 20:35 ` Mike Kravetz
2018-05-23 11:18 ` Vlastimil Babka
2018-05-23 18:07 ` Reinette Chatre
2018-05-28 13:12 ` Vlastimil Babka
2018-05-03 23:29 ` [PATCH v2 4/4] mm/hugetlb: use find_alloc_contig_pages() to allocate gigantic pages Mike Kravetz
2018-05-21 12:00 ` [PATCH v2 0/4] Interface for higher order contiguous allocations Vlastimil Babka
2018-05-22 0:15 ` Mike Kravetz
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