linux-kernel - Re: [PATCH 2/3] mm: add find_alloc_contig

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Message-ID: <20180424133740.GH17484@dhcp22.suse.cz>
Date:   Tue, 24 Apr 2018 07:37:40 -0600
From:   Michal Hocko <mhocko@...nel.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org,
        Reinette Chatre <reinette.chatre@...el.com>,
        Christopher Lameter <cl@...ux.com>,
        Guy Shattah <sguy@...lanox.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Michal Nazarewicz <mina86@...a86.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Nellans <dnellans@...dia.com>,
        Laura Abbott <labbott@...hat.com>, Pavel Machek <pavel@....cz>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/3] mm: add find_alloc_contig_pages() interface

On Sun 22-04-18 21:22:07, Mike Kravetz wrote:
> On 04/22/2018 05:09 PM, Michal Hocko wrote:
[...
> > Also do we want to check other usual suspects? E.g. PageReserved? And
> > generally migrateable pages if page count > 0. Or do we want to leave
> > everything to the alloc_contig_range?
> 
> I think you proposed something like the above with limited checking at
> some time in the past.  In my testing, allocations were more likely to
> succeed if we did limited testing here and let alloc_contig_range take
> a shot at migration/allocation.  There really are two ways to approach
> this, do as much checking up front or let it be handled by alloc_contig_range.

OK, it would be great to have a comment mentioning that. The discrepancy
will just hit eyes 

[...]
> Unless I am missing something, calls to alloc_contig range need to have
> a size that is a multiple of page block.  This is because isolation needs
> to take place at a page block level.  We can easily 'round up' and release
> excess pages.

I am not sure but can we simply leave a part of the page block behind? I
mean it might have a misleading migrate type but that shouldn't matter
much, no?

Thanks!
-- 
Michal Hocko
SUSE Labs