linux-kernel - Re: [PATCH RFC] mm/madvise: introduce MADV

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Date:   Thu, 18 Feb 2021 11:54:48 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Oscar Salvador <osalvador@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Minchan Kim <minchan@...nel.org>, Jann Horn <jannh@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Dave Hansen <dave.hansen@...el.com>,
        Hugh Dickins <hughd@...gle.com>,
        Rik van Riel <riel@...riel.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>, Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>, linux-alpha@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH RFC] mm/madvise: introduce MADV_POPULATE to
 prefault/prealloc memory

>>>      If we hit
>>>      hardware errors on pages, ignore them - nothing we really can or
>>>      should do.
>>> 3. On errors during MADV_POPULATED, some memory might have been
>>>      populated. Callers have to clean up if they care.
>>
>> How does caller find out? madvise reports 0 on success so how do you
>> find out how much has been populated?
> 
> If there is an error, something might have been populated. In my QEMU
> implementation, I simply discard the range again, good enough. I don't
> think we need to really indicate "error and populated" or "error and not
> populated".

Clarifying again: if madvise(MADV_POPULATED) succeeds, it returns 0. If 
there was a problem poopulating memory, it returns -ENOMEM (similar to 
MADV_WILLNEED). Callers can detect the error and discard.

-- 
Thanks,

David / dhildenb