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Date:   Mon, 5 Aug 2019 19:28:34 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc:     Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Chris Wilson <chris@chris-wilson.co.uk>,
        David Howells <dhowells@redhat.com>,
        Christoph Hellwig <hch@lst.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Hugh Dickins <hughd@google.com>
Subject: Re: [PATCHv2 2/3] i915: convert to new mount API
Message-ID: <20190805182834.GI1131@ZenIV.linux.org.uk>
References: <20190805160307.5418-1-sergey.senozhatsky@gmail.com>
 <20190805160307.5418-3-sergey.senozhatsky@gmail.com>
 <20190805181255.GH1131@ZenIV.linux.org.uk>
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On Mon, Aug 05, 2019 at 07:12:55PM +0100, Al Viro wrote:
> On Tue, Aug 06, 2019 at 01:03:06AM +0900, Sergey Senozhatsky wrote:
> > tmpfs does not set ->remount_fs() anymore and its users need
> > to be converted to new mount API.
> 
> Could you explain why the devil do you bother with remount at all?
> Why not pass the right options when mounting the damn thing?

... and while we are at it, I really wonder what's going on with
that gemfs thing - among the other things, this is the only
user of shmem_file_setup_with_mnt().  Sure, you want your own
options, but that brings another question - is there any reason
for having the huge=... per-superblock rather than per-file?

After all, the readers of ->huge in mm/shmem.c are
mm/shmem.c:582:     (shmem_huge == SHMEM_HUGE_FORCE || sbinfo->huge) &&
	is_huge_enabled(), sbinfo is an explicit argument

mm/shmem.c:1799:        switch (sbinfo->huge) {
	shmem_getpage_gfp(), sbinfo comes from inode

mm/shmem.c:2113:                if (SHMEM_SB(sb)->huge == SHMEM_HUGE_NEVER)
	shmem_get_unmapped_area(), sb comes from file

mm/shmem.c:3531:        if (sbinfo->huge)
mm/shmem.c:3532:                seq_printf(seq, ",huge=%s", shmem_format_huge(sbinfo->huge));
	->show_options()
mm/shmem.c:3880:        switch (sbinfo->huge) {
	shmem_huge_enabled(), sbinfo comes from an inode

And the only caller of is_huge_enabled() is shmem_getattr(), with sbinfo
picked from inode.

So is there any reason why the hugepage policy can't be per-file, with
the current being overridable default?