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* [PATCH V3 0/4] Reducing parameters of alloc_pages* family of functions
@ 2014-12-12 16:13 Vlastimil Babka
  2014-12-12 16:13 ` [PATCH V3 1/4] mm: set page->pfmemalloc in prep_new_page() Vlastimil Babka
                   ` (4 more replies)
  0 siblings, 5 replies; 9+ messages in thread
From: Vlastimil Babka @ 2014-12-12 16:13 UTC (permalink / raw)
  To: Andrew Morton, linux-mm
  Cc: linux-kernel, Linus Torvalds, Vlastimil Babka, Aneesh Kumar K.V,
	David Rientjes, Johannes Weiner, Joonsoo Kim, Kirill A. Shutemov,
	Mel Gorman, Michal Hocko, Minchan Kim, Rik van Riel,
	Zhang Yanfei

Hey all,

this is a V3 of attempting something that has been discussed when Minchan
proposed to expand the x86 kernel stack [1], namely the reduction of huge
number of parameters that the alloc_pages* family and get_page_from_freelist()
functions have.

The result is this series, ordered in the subjective importance of the patches.

The series is based on mmotm-2014-12-02-15-55 and I use gcc 4.8.3 20140627 on
openSUSE 13.2. Config includess NUMA and COMPACTION. It also applies to
next-20141212.

Changes since v2:
o Per Linus's suggestion, removed order from alloc_context due to poor
  conceptual fit. Interestingly, this improved the stack/code size a bit.
o Attempted to merge migratetype into alloc_flags, but it was ugly and made
  things only worse. So I didn't even attempt to merge order there.

The core is 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.

First, let's look at the code size savings by bloat-o-meter, as the patches
stack up:

Patch 1 (vs mmotm):

function                                     old     new   delta
get_page_from_freelist                      2554    2490     -64

Patch 2:

function                                     old     new   delta
__alloc_pages_nodemask                       571    2220   +1649
get_page_from_freelist                      2490    2560     +70
__alloc_pages_direct_compact                 332     302     -30
__alloc_pages_slowpath                      1878       -   -1878

Here gcc decided to inline _slowpath, so let's try comparing with Patch 1
plus forced inline of _slowpath:

add/remove: 0/0 grow/shrink: 1/2 up/down: 70/-428 (-358)
function                                     old     new   delta
get_page_from_freelist                      2490    2560     +70
__alloc_pages_direct_compact                 332     284     -48
__alloc_pages_nodemask                      2618    2194    -424

Looks like get_page_from_freelist() did benefit from getting the parameters
separately, but overal it's a win.

Patch 3:

__alloc_pages_direct_compact                 284     256     -28
try_to_compact_pages                         582     566     -16

A tiny overal win.

Patch 4:

function                                     old     new   delta
__alloc_pages_nodemask                      2194    2191      -3
nr_free_zone_pages                           129     115     -14
get_page_from_freelist                      2560    2505     -55
try_to_compact_pages                         566     579     +13

Small overal win. A few more object files should be also affected,
but were not tested.

Now stack sizes per ./scripts/checkstack.pl:

                        mmotm    P1   P2
__alloc_pages_slowpath    176   176    -
get_page_from_freelist:   160   152  160
__alloc_pages_nodemask    104   104  168 
__alloc_pages_direct_c     32    32   16

Patch 1 saves a bit, Patch 2 result muddled by inlining.
Again, let's use Patch 1 + forced inline as baseline for the rest:

                          P1i    P2    P3    P4
__alloc_pages_nodemask    240   168   168   168
get_page_from_freelist:   152   160   160   160
try_to_compact_pages       64    64    56    56
__alloc_pages_direct_c     32    16     -     -

Again, Patch 2 bloats get_page_from_freelist(), but overal is a win. The
rest almost doesn't affect stack usage.

[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 |  15 ++-
 include/linux/mm.h         |  14 +++
 include/linux/mmzone.h     |  13 +--
 mm/compaction.c            |  23 ++---
 mm/mmzone.c                |   4 +-
 mm/page_alloc.c            | 250 +++++++++++++++++++--------------------------
 6 files changed, 144 insertions(+), 175 deletions(-)

-- 
2.1.2

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^ permalink raw reply	[flat|nested] 9+ messages in thread
end of thread, other threads:[~2015-01-07  4:53 UTC | newest]

Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2014-12-12 16:13 [PATCH V3 0/4] Reducing parameters of alloc_pages* family of functions Vlastimil Babka
2014-12-12 16:13 ` [PATCH V3 1/4] mm: set page->pfmemalloc in prep_new_page() Vlastimil Babka
2014-12-12 16:13 ` [PATCH V3 2/4] mm, page_alloc: reduce number of alloc_pages* functions' parameters Vlastimil Babka
2014-12-12 16:13 ` [PATCH V3 3/4] mm: reduce try_to_compact_pages parameters Vlastimil Babka
2014-12-12 16:13 ` [PATCH V3 4/4] mm: microoptimize zonelist operations Vlastimil Babka
2014-12-18 21:26 ` [PATCH V3 0/4] Reducing parameters of alloc_pages* family of functions Andrew Morton
2015-01-05 14:22   ` Vlastimil Babka
2015-01-05 16:01     ` Vlastimil Babka
2015-01-07  4:53       ` Linus Torvalds

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