linux-kernel - Re: [RFC PATCH] mm: align anon mmap for THP

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Message-ID: <20190114180230.GN21345@dhcp22.suse.cz>
Date:   Mon, 14 Jan 2019 19:02:30 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     "Harrosh, Boaz" <Boaz.Harrosh@...app.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        Toshi Kani <toshi.kani@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH] mm: align anon mmap for THP

On Mon 14-01-19 16:54:02, Harrosh, Boaz wrote:
> Michal Hocko <mhocko@...nel.org> wrote:
[...]
> >> We run with our own compiled Kernel on various distros, THP is configured
> >> in but mmap against /dev/shm/ never gives me Huge pages. Does it only
> >> work with unanimous mmap ? (I think it is mount dependent which is not
> >> in the application control)
> >
> > If you are talking about THP then you have to enable huge pages for the
> > mapping AFAIR.
> 
> This is exactly what I was looking to achieve but was not able to do. Most probably
> a stupid omission on my part, but just to show that it is not that trivial and strait
> out-of-the-man-page way to do it.  (Would love a code snippet if you ever wrote one?)

Have you tried
mount -t tmpfs -o huge=always none $MNT_POINT ?

It is true that man pages are silent about this but at least Documentation/admin-guide/mm/transhuge.rst
has an information. Time to send a patch to man pages I would say.
-- 
Michal Hocko
SUSE Labs