[PATCH] Resolve LRU page-pinning issue for file-backed pages

[Chris Goldsworthy <cgoldswo@codeaurora.org>]

It is possible for file-backed pages to end up in a contiguous memory
area (CMA), such that the relevant page must be migrated using the
.migratepage() callback when its backing physical memory is selected
for use in an CMA allocation (through cma_alloc()).  However, if a set
of address space operations (AOPs) for a file-backed page lacks a
migratepage() page call-back, fallback_migrate_page() will be used
instead, which through try_to_release_page() calls
try_to_free_buffers() (which is called directly or through a
try_to_free_buffers() callback.  try_to_free_buffers() in turn calls
drop_buffers().

drop_buffers() itself can fail due to the buffer_head associated with
a page being busy. However, it is possible that the buffer_head is on
an LRU list for a CPU, such that we can try removing the buffer_head
from that list, in order to successfully release the page.  Do this.
For reference ext4_journalled_aops is a set of AOPs that lacks the
migratepage() callback.

Laura Abbott (1):
  fs/buffer.c: Revoke LRU when trying to drop buffers

 fs/buffer.c | 47 +++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 45 insertions(+), 2 deletions(-)

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