linux-kernel - Re: [PATCH] shmem: avoid huge pages for small files

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Date:   Fri, 21 Oct 2016 17:12:41 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Dave Chinner <david@...morbit.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Hugh Dickins <hughd@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] shmem: avoid huge pages for small files

On Fri 21-10-16 18:00:07, Kirill A. Shutemov wrote:
> On Fri, Oct 21, 2016 at 04:01:18PM +1100, Dave Chinner wrote:
[...]
> > None of these aspects can be optimised sanely by a single threshold,
> > especially when considering the combination of access patterns vs file
> > layout.
> 
> I agree.
> 
> Here I tried to address the particular performance regression I see with
> huge pages enabled on tmpfs. It doesn't mean to fix all possible issues.

So can we start simple and use huge pages on shmem mappings only when
they are larger than the huge page? Without any tunable which might turn
out to be misleading/wrong later on. If I understand Dave's comments it
is really not all that clear that a mount option makes sense. I cannot
comment on those but they clearly show that there are multiple points of
view here.
-- 
Michal Hocko
SUSE Labs