linux-kernel - Re: [PATCH v2] mm,thp,shmem: limit shmem THP alloc gfp

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Date:   Fri, 23 Oct 2020 10:49:56 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Rik van Riel <riel@...riel.com>
Cc:     Hugh Dickins <hughd@...gle.com>, Yu Xu <xuyu@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-mm@...ck.org, kernel-team@...com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm,thp,shmem: limit shmem THP alloc gfp_mask

On Thu 22-10-20 23:40:53, Rik van Riel wrote:
> On Thu, 2020-10-22 at 19:54 -0700, Hugh Dickins wrote:
[...]
> > But it's likely that they have accumulated some defrag wisdom, which
> > tmpfs can take on board - but please accept that in using a huge
> > mount,
> > the preference for huge has already been expressed, so I don't expect
> > anon THP alloc_hugepage_direct_gfpmask() choices will map one to one.
> 
> In my mind, the huge= mount options for tmpfs corresponded
> to the "enabled" anon THP options, denoting a desired end
> state, not necessarily how much we will stall allocations
> to get there immediately.

It is really unfortunate that our configuration space is so huge and
messy but we have to live with that now.

Anyway, I would tend to agree that with an absense of per-mount defrag
configuration it makes sense to use the global one. Is anybody aware of
usecases where a mount specific configuration would make sense?
-- 
Michal Hocko
SUSE Labs