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From: David Hildenbrand <david@redhat.com>
To: Oscar Salvador <osalvador@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Muchun Song <songmuchun@bytedance.com>,
	Michal Hocko <mhocko@kernel.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/2] mm: Make alloc_contig_range handle free hugetlb pages
Date: Thu, 4 Mar 2021 11:32:29 +0100	[thread overview]
Message-ID: <4ede47fd-d01e-6d9c-288a-2ec97b5392af@redhat.com> (raw)
In-Reply-To: <YEC0ODM5gtEU+JqN@localhost.localdomain>

>> I think we should not swallo such return values in
>> isolate_or_dissolve_huge_page() and instead properly report esp. -ENOMEM
>> properly up this callchain now. Otherwise we'll end up retrying / reporting
>> -EBUSY, which is misleading.
> 
> I am not sure I follow you here.
> So, atm, alloc_and_dissolve_huge_page can either generate -ENOMEM or
> -EBUSY wrt. error codes.
> -ENOMEM when we cannot allocate a page, and -EBUSY when we raced with
> someone.
> You mean to only report ENOMEM down the chain?

Yes, fatal errors.

> 
>>  From isolate_migratepages_range()/isolate_migratepages_block() we'll keep
>> reporting "pfn > 0".
>>
>> a) In isolate_migratepages_range() we'll keep iterating over pageblocks
>> although we should just fail with -ENOMEM right away.
>>
>> b) In __alloc_contig_migrate_range() we'll keep retrying up to 5 times
>> although we should just fail with -ENOMEM. We end up returning "-EBUSY"
>> after retrying.
>>
>> c) In alloc_contig_range() we'll continue trying to isolate although we
>> should just return -ENOMEM.
> 
> Yes, "fatal" errors get masked, and hence we treat everything as "things
> are busy, let us try again", and this is rather unforunate.
> 
>> I think we have should start returning proper errors from
>> isolate_migratepages_range()/isolate_migratepages_block() on critical issues
>> (-EINTR, -ENOMEM) instead of going via "!pfn vs. pfn" and retrying on "pfn".
>>
>> So we should then fail with -ENOMEM during isolate_migratepages_range()
>> cleanly, just as we would do when we get -ENOMEM during migrate_pages().
> 
> I guess we could rework the interface and make isolate_migratepages_range and
> isolate_migratepages_block to report the right thing.
> I yet have to check that this does not mess up a lot with the compaction
> interface.
> 
> But overall I agree with your point here, and I am willing to to tackle
> this.
> 
> The question is whether we want to do this as part of this series, or
> after this series gets picked up.
> IMHO, we could do it after, as a follow-up, unless you feel strong about
> it.
> 
> What do you think?

I think this is now the second fatal error we can have (-EINTR, 
-ENOMEM), thus the current interface (return "NULL" on fatal errros) no 
longer works properly.

No strong opinion about fixing this up on top - could be it's cleaner to 
just do it right away.

-- 
Thanks,

David / dhildenb



  reply	other threads:[~2021-03-04 10:32 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-22 13:51 [PATCH v3 0/2] Make alloc_contig_range handle Hugetlb pages Oscar Salvador
2021-02-22 13:51 ` [PATCH v3 1/2] mm: Make alloc_contig_range handle free hugetlb pages Oscar Salvador
2021-02-25 20:03   ` Mike Kravetz
2021-02-26  9:48     ` Oscar Salvador
2021-02-26  8:35   ` Michal Hocko
2021-02-26  8:38     ` Michal Hocko
2021-02-26  9:25       ` David Hildenbrand
2021-02-26  9:47         ` Oscar Salvador
2021-02-26  9:45     ` Oscar Salvador
2021-02-26  9:51       ` Michal Hocko
2021-03-01 14:09   ` David Hildenbrand
2021-03-04 10:19     ` Oscar Salvador
2021-03-04 10:32       ` David Hildenbrand [this message]
2021-03-04 10:41         ` Oscar Salvador
2021-02-22 13:51 ` [PATCH v3 2/2] mm: Make alloc_contig_range handle in-use " Oscar Salvador
2021-02-25 23:05   ` Mike Kravetz
2021-02-26  8:46   ` Michal Hocko
2021-02-26 10:24     ` Oscar Salvador
2021-02-26 10:27       ` Oscar Salvador
2021-02-26 12:46       ` Michal Hocko
2021-02-28 13:43         ` Oscar Salvador
2021-03-05 17:30   ` David Hildenbrand
2021-03-01 12:43 ` [PATCH v3 0/2] Make alloc_contig_range handle Hugetlb pages David Hildenbrand
2021-03-01 12:57   ` Oscar Salvador
2021-03-01 12:59     ` David Hildenbrand

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