memcg: revert gfp mask fix

My patch, memcg-fix-gfp_mask-of-callers-of-charge.patch changed gfp_mask
of callers of charge to be GFP_HIGHUSER_MOVABLE for showing what will
happen at memory reclaim.

But in recent discussion, it's NACKed because it sounds ugly.

This patch is for reverting it and add some clean up to gfp_mask of
callers of charge.  No behavior change but need review before generating
HUNK in deep queue.

This patch also adds explanation to meaning of gfp_mask passed to charge
functions in memcontrol.h.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 2fdd138..59ac95a 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -26,6 +26,16 @@ struct page;
 struct mm_struct;
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
+/*
+ * All "charge" functions with gfp_mask should use GFP_KERNEL or
+ * (gfp_mask & GFP_RECLAIM_MASK). In current implementatin, memcg doesn't
+ * alloc memory but reclaims memory from all available zones. So, "where I want
+ * memory from" bits of gfp_mask has no meaning. So any bits of that field is
+ * available but adding a rule is better. charge functions' gfp_mask should
+ * be set to GFP_KERNEL or gfp_mask & GFP_RECLAIM_MASK for avoiding ambiguous
+ * codes.
+ * (Of course, if memcg does memory allocation in future, GFP_KERNEL is sane.)
+ */
 
 extern int mem_cgroup_newpage_charge(struct page *page, struct mm_struct *mm,
 				gfp_t gfp_mask);