From 2b108268006e06d57ec9810f4ccf5d99d7e5b598 Mon Sep 17 00:00:00 2001
From: Chris Mason <clm@fb.com>
Date: Mon, 6 Apr 2015 07:48:20 -0700
Subject: [PATCH] Btrfs: don't use highmem for free space cache pages

In order to create the free space cache concurrently with FS modifications,
we need to take a few block group locks.

The cache code also does kmap, which would schedule with the locks held.
Instead of going through kmap_atomic, lets just use lowmem for the cache
pages.

Signed-off-by: Chris Mason <clm@fb.com>
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