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Message-Id: <1420713191-17509-1-git-send-email-vbabka@suse.cz>
Date: Thu, 8 Jan 2015 11:33:07 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
Vlastimil Babka <vbabka@...e.cz>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
David Rientjes <rientjes@...gle.com>,
Johannes Weiner <hannes@...xchg.org>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
Minchan Kim <minchan@...nel.org>,
Rik van Riel <riel@...hat.com>,
Zhang Yanfei <zhangyanfei@...fujitsu.com>
Subject: [PATCH V5 0/4] Reducing parameters of alloc_pages* family of functions
Changes since v4:
o Documented where struct alloc_context fields change per Michal's suggestion.
o Rebased on next-20150108. Relative improvements went down for code again,
but up for stack. And finally I didn't have to mess with _slowpath inlining
anymore for the comparison as it was already being inlined in the baseline.
Changes since v3:
o Moved struct alloc_context definition to mm/internal.h
o Rebased on latest -next and re-measured. Sadly, the code/stack size
improvements are smaller with the new baseline.
The possibility of replacing the numerous parameters of alloc_pages* functions
with a single structure has been discussed when Minchan proposed to expand the
x86 kernel stack [1]. This series implements the change, along with few more
cleanups/microoptimizations.
The series is based on next-20150108 and I used gcc 4.8.3 20140627 on openSUSE
13.2 for compiling. Config includess NUMA and COMPACTION.
The core change is the introduction of a new struct alloc_context, which looks
like this:
struct alloc_context {
struct zonelist *zonelist;
nodemask_t *nodemask;
struct zone *preferred_zone;
int classzone_idx;
int migratetype;
enum zone_type high_zoneidx;
};
All the contents is mostly constant, except that __alloc_pages_slowpath()
changes preferred_zone, classzone_idx and potentially zonelist. But that's not
a problem in case control returns to retry_cpuset: in __alloc_pages_nodemask(),
those will be reset to initial values again (although it's a bit subtle).
On the other hand, gfp_flags and alloc_info mutate so much that it doesn't
make sense to put them into alloc_context. Still, the result is one parameter
instead of up to 7. This is all in Patch 2.
Patch 3 is a step to expand alloc_context usage out of page_alloc.c itself.
The function try_to_compact_pages() can also much benefit from the parameter
reduction, but it means the struct definition has to be moved to a shared
header.
Patch 1 should IMHO be included even if the rest is deemed not useful enough.
It improves maintainability and also has some code/stack reduction. Patch 4
is OTOH a tiny optimization.
Overall bloat-o-meter results:
add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-460 (-460)
function old new delta
nr_free_zone_pages 129 115 -14
__alloc_pages_direct_compact 329 256 -73
get_page_from_freelist 2670 2576 -94
__alloc_pages_nodemask 2564 2285 -279
try_to_compact_pages 582 579 -3
Overall stack sizes per ./scripts/checkstack.pl:
old new delta
get_page_from_freelist: 184 184 0
__alloc_pages_nodemask 248 200 -48
__alloc_pages_direct_c 40 - -40
try_to_compact_pages 72 72 0
-88
[1] http://marc.info/?l=linux-mm&m=140142462528257&w=2
Vlastimil Babka (4):
mm: set page->pfmemalloc in prep_new_page()
mm, page_alloc: reduce number of alloc_pages* functions' parameters
mm: reduce try_to_compact_pages parameters
mm: microoptimize zonelist operations
include/linux/compaction.h | 17 ++--
include/linux/mmzone.h | 13 +--
mm/compaction.c | 23 ++---
mm/internal.h | 22 ++++
mm/mmzone.c | 4 +-
mm/page_alloc.c | 245 +++++++++++++++++++--------------------------
6 files changed, 152 insertions(+), 172 deletions(-)
--
2.1.2
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