Re: [RFC PATCH 0/5] mm, hugetlb: allocation API and migration improvements

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On 12/15/2017 06:33 PM, Michal Hocko wrote:
> Naoya,
> this has passed Mike's review (thanks for that!), you have mentioned
> that you can pass this through your testing machinery earlier. While
> I've done some testing already I would really appreciate if you could
> do that as well. Review would be highly appreciated as well.

Sorry for my slow response. I reviewed/tested this patchset and looks
good to me overall.

I have one comment on the code path from mbind(2).
The callback passed to migrate_pages() in do_mbind() (i.e. new_page())
calls alloc_huge_page_noerr() which currently doesn't call SetPageHugeTemporary(),
so hugetlb migration fails when h->surplus_huge_page >= h->nr_overcommit_huge_pages.

I don't think this is a bug, but it would be better if mbind(2) works
more similarly with other migration callers like move_pages(2)/migrate_pages(2).

Thanks,
Naoya Horiguchi


> 
> Thanks!
> 
> On Mon 04-12-17 15:01:12, Michal Hocko wrote:
>> Hi,
>> this is a follow up for [1] for the allocation API and [2] for the
>> hugetlb migration. It wasn't really easy to split those into two
>> separate patch series as they share some code.
>>
>> My primary motivation to touch this code is to make the gigantic pages
>> migration working. The giga pages allocation code is just too fragile
>> and hacked into the hugetlb code now. This series tries to move giga
>> pages closer to the first class citizen. We are not there yet but having
>> 5 patches is quite a lot already and it will already make the code much
>> easier to follow. I will come with other changes on top after this sees
>> some review.
>>
>> The first two patches should be trivial to review. The third patch
>> changes the way how we migrate huge pages. Newly allocated pages are a
>> subject of the overcommit check and they participate surplus accounting
>> which is quite unfortunate as the changelog explains. This patch doesn't
>> change anything wrt. giga pages.
>> Patch #4 removes the surplus accounting hack from
>> __alloc_surplus_huge_page.  I hope I didn't miss anything there and a
>> deeper review is really due there.
>> Patch #5 finally unifies allocation paths and giga pages shouldn't be
>> any special anymore. There is also some renaming going on as well.
>>
>> Shortlog
>> Michal Hocko (5):
>>       mm, hugetlb: unify core page allocation accounting and initialization
>>       mm, hugetlb: integrate giga hugetlb more naturally to the allocation path
>>       mm, hugetlb: do not rely on overcommit limit during migration
>>       mm, hugetlb: get rid of surplus page accounting tricks
>>       mm, hugetlb: further simplify hugetlb allocation API
>>
>> Diffstat:
>>  include/linux/hugetlb.h |   3 +
>>  mm/hugetlb.c            | 305 +++++++++++++++++++++++++++---------------------
>>  mm/migrate.c            |   3 +-
>>  3 files changed, 175 insertions(+), 136 deletions(-)
>>
>>
>> [1] http://lkml.kernel.org/r/20170622193034.28972-1-mhocko@kernel.org
>> [2] http://lkml.kernel.org/r/20171122152832.iayefrlxbugphorp@dhcp22.suse.cz
>>
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