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-20150105 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: 0/1 grow/shrink: 1/3 up/down: 1587/-1941 (-354)
function old new delta
__alloc_pages_nodemask 589 2176 +1587
nr_free_zone_pages 129 115 -14
__alloc_pages_direct_compact 329 256 -73
get_page_from_freelist 2670 2576 -94
__alloc_pages_slowpath 1760 - -1760
try_to_compact_pages 582 579 -3
Overal bloat-o-meter with forced inline in baseline, for fair comparison:
add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-512 (-512)
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 2507 2176 -331
try_to_compact_pages 582 579 -3
Overall stack sizes per ./scripts/checkstack.pl:
old new delta
__alloc_pages_slowpath 152 - -152
get_page_from_freelist: 184 184 0
__alloc_pages_nodemask 120 184 +64
__alloc_pages_direct_c 40 40 -40
try_to_compact_pages 72 72 0
-128
Again with forced inline on baseline:
old new delta
get_page_from_freelist: 184 184 0
__alloc_pages_nodemask 216 184 -32
__alloc_pages_direct_c 40 - -40
try_to_compact_pages 72 72 0
-72
[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 | 14 +++
mm/mmzone.c | 4 +-
mm/page_alloc.c | 245 +++++++++++++++++++--------------------------
6 files changed, 144 insertions(+), 172 deletions(-)
--
2.1.2
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