Re: [PATCH 0/2] new API to allocate buffer-cache for superblock in non-movable area

From: Peter Zijlstra
Date: Wed Jul 30 2014 - 06:19:53 EST

On Wed, Jul 30, 2014 at 12:11:43PM +0200, Jan Kara wrote:
> > sb_bread allocates page from movable area but it is not movable until the
> > reference counter of the buffer-head becomes zero.
> > There is no lock for the buffer but the reference counter acts like lock.
> OK, but why do you care about a single page (of at most handful if you
> have more filesystems) which isn't movable? That shouldn't make a big
> difference to compaction...

The thing is, CMA _must_ be able to clear all the pages in its range,
otherwise its broken.

So placing nonmovable pages in a movable block utterly wrecks that.

Now, Ted said that there's more effectively pinned stuff from
filesystems (and I imagine those would be things like the root inode
etc.) and those would equally wreck this..

But Gioh didn't mention any of that.. he should I suppose.

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