Re: [PATCH] undo the brd.c part of ramfs-and-ram-disk-pages-are-unevictable.patch

[Nick Piggin]

On Friday 13 June 2008 05:00, Lee Schermerhorn wrote:
> On Thu, 2008-06-12 at 13:53 -0400, Rik van Riel wrote:
> > Undo the brd.c part of ramfs-and-ram-disk-pages-are-unevictable.patch.
> > The brd pages do not live on the LRU at all, so there is no need to
> > play these tricks.
>
> Does this mean that these pages cannot be migrated?  E.g., to evacuate
> memory for hotplug?  Looks like all paths to migrate_pages() construct a
> list of pages to migrate by isolating them from the lru
> [isolate_lru_page()].  Any pages not found in the lru are skipped.

Yes. They have nothing to do with user pages or pagecache pages at all
really. brd is now a properly layered block device driver that does not
know anything about buffer cache ;)

You can think of the pages it allocates as completely private, and they
are used to implement the backing store for the block device.

The vm/fs layers will instantiate buffer cache over this device, which
is reclaimable.
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