linux-kernel - Re: [RFC PATCH 3/3] mm, proc: report PR_SET_THP

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Date:   Tue, 27 Nov 2018 17:25:44 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     William Kucharski <william.kucharski@...cle.com>
Cc:     linux-api@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 3/3] mm, proc: report PR_SET_THP_DISABLE in proc

On Tue 27-11-18 07:50:08, William Kucharski wrote:
> 
> 
> > On Nov 27, 2018, at 6:17 AM, Michal Hocko <mhocko@...nel.org> wrote:
> > 
> > This is only about the process wide flag to disable THP. I do not see
> > how this can be alighnement related. I suspect you wanted to ask in the
> > smaps patch?
> 
> No, answered below.
> 
> > 
> >> I'm having to deal with both these issues in the text page THP
> >> prototype I've been working on for some time now.
> > 
> > Could you be more specific about the issue and how the alignment comes
> > into the game? The only thing I can think of is to not report VMAs
> > smaller than the THP as eligible. Is this what you are looking for?
> 
> Basically, if the faulting VA is one that cannot be mapped with a THP
> due to alignment or size constraints, it may be "eligible" for THP
> mapping but ultimately can't be.
> 
> I was just double checking that this was meant to be more of a check done
> before code elsewhere performs additional checks and does the actual THP
> mapping, not an all-encompassing go/no go check for THP mapping.

I am still not sure I follow you completely here. This just reports
per-task eligibility. The system wide eligibility is reported via sysfs
and the per vma eligibility is reported via /proc/<pid>/smaps.

-- 
Michal Hocko
SUSE Labs