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Shaohua Li 76a33fc380 vmscan: prevent get_scan_ratio() rounding errors 
get_scan_ratio() calculates percentage and if the percentage is < 1%, it
will round percentage down to 0% and cause we completely ignore scanning
anon/file pages to reclaim memory even the total anon/file pages are very
big.

To avoid underflow, we don't use percentage, instead we directly calculate
how many pages should be scaned.  In this way, we should get several
scanned pages for < 1% percent.

This has some benefits:

1. increase our calculation precision

2.  making our scan more smoothly.  Without this, if percent[x] is
   underflow, shrink_zone() doesn't scan any pages and suddenly it scans
   all pages when priority is zero.  With this, even priority isn't zero,
   shrink_zone() gets chance to scan some pages.

Note, this patch doesn't really change logics, but just increase
precision.  For system with a lot of memory, this might slightly changes
behavior.  For example, in a sequential file read workload, without the
patch, we don't swap any anon pages.  With it, if anon memory size is
bigger than 16G, we will see one anon page swapped.  The 16G is calculated
as PAGE_SIZE * priority(4096) * (fp/ap).  fp/ap is assumed to be 1024
which is common in this workload.  So the impact sounds not a big deal.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-05-25 08:07:00 -07:00
..
backing-dev.c writeback: fixups for !dirty_writeback_centisecs 2010-05-21 20:00:35 +02:00
bootmem.c Merge branch 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/x86/linux-2.6-tip 2010-04-07 11:02:23 -07:00
bounce.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
compaction.c mm: compaction: add a tunable that decides when memory should be compacted and when it should be reclaimed 2010-05-25 08:06:59 -07:00
debug-pagealloc.c generic debug pagealloc 2009-04-01 08:59:13 -07:00
dmapool.c dmapools: protect page_list walk in show_pools() 2009-06-30 18:56:00 -07:00
fadvise.c readahead: introduce FMODE_RANDOM for POSIX_FADV_RANDOM 2010-03-06 11:26:25 -08:00
failslab.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
filemap.c cpuset,mm: fix no node to alloc memory when changing cpuset's mems 2010-05-25 08:06:57 -07:00
filemap_xip.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
fremap.c mm: clean up mm_counter 2010-03-06 11:26:23 -08:00
highmem.c grammar fix in comment 2010-02-05 12:22:40 +01:00
hugetlb.c cpuset,mm: fix no node to alloc memory when changing cpuset's mems 2010-05-25 08:06:57 -07:00
hwpoison-inject.c HWPOISON: Don't do early filtering if filter is disabled 2009-12-16 12:20:01 +01:00
init-mm.c mm: consolidate init_mm definition 2009-06-16 19:47:28 -07:00
internal.h HWPOISON: add an interface to switch off/on all the page filters 2009-12-16 12:19:59 +01:00
Kconfig mm: allow CONFIG_MIGRATION to be set without CONFIG_NUMA or memory hot-remove 2010-05-25 08:06:59 -07:00
Kconfig.debug trivial: improve help text for mm debug config options 2009-09-21 15:14:57 +02:00
kmemcheck.c kmemcheck: Fix build errors due to missing slab.h 2010-03-30 22:02:32 +09:00
kmemleak-test.c percpu: clean up percpu variable definitions 2009-06-24 15:13:48 +09:00
kmemleak.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
ksm.c mm: migration: share the anon_vma ref counts between KSM and page migration 2010-05-25 08:06:58 -07:00
maccess.c maccess,probe_kernel: Allow arch specific override probe_kernel_(read|write) 2010-01-07 11:58:36 -06:00
madvise.c HWPOISON: Add a madvise() injector for soft page offlining 2009-12-16 12:20:00 +01:00
Makefile mm: compaction: memory compaction core 2010-05-25 08:06:59 -07:00
memcontrol.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2010-05-20 09:20:59 -07:00
memory-failure.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
memory.c mm: avoid null-pointer deref in sync_mm_rss() 2010-04-07 08:38:02 -07:00
memory_hotplug.c mm: introduce dump_page() and print symbolic flag names 2010-03-12 15:52:28 -08:00
mempolicy.c mm: consider the entire user address space during node migration 2010-05-25 08:07:00 -07:00
mempool.c mm: remove broken 'kzalloc' mempool 2009-09-22 07:17:35 -07:00
migrate.c mm: compaction: memory compaction core 2010-05-25 08:06:59 -07:00
mincore.c mincore: do nested page table walks 2010-05-25 08:06:58 -07:00
mlock.c x86, perf, bts, mm: Delete the never used BTS-ptrace code 2010-03-26 11:33:55 +01:00
mm_init.c
mmap.c mmap: check ->vm_ops before dereferencing 2010-04-27 08:26:51 -07:00
mmu_context.c exit: fix oops in sync_mm_rss 2010-03-24 16:31:21 -07:00
mmu_notifier.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
mmzone.c [ARM] Double check memmap is actually valid with a memmap has unexpected holes V2 2009-05-18 11:22:24 +01:00
mprotect.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
mremap.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
msync.c sanitize vfs_fsync calling conventions 2010-05-21 18:31:21 -04:00
nommu.c NOMMU: Fix __get_user_pages() to pin last page on offset buffers 2010-03-25 14:13:27 -07:00
oom_kill.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
page-writeback.c writeback: fix mixed up arguments to bdi_start_writeback() 2010-05-21 20:01:54 +02:00
page_alloc.c mm: compaction: defer compaction using an exponential backoff when compaction fails 2010-05-25 08:07:00 -07:00
page_cgroup.c memcg: avoid use cmpxchg in swap cgroup maintainance 2010-03-17 18:43:47 -07:00
page_io.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
page_isolation.c
pagewalk.c pagemap: fix pfn calculation for hugepage 2010-04-07 08:38:04 -07:00
percpu-km.c percpu: implement kernel memory based chunk allocation 2010-05-01 08:30:50 +02:00
percpu-vm.c percpu: move vmalloc based chunk management into percpu-vm.c 2010-05-01 08:30:50 +02:00
percpu.c percpu: implement kernel memory based chunk allocation 2010-05-01 08:30:50 +02:00
percpu_up.c percpu: don't implicitly include slab.h from percpu.h 2010-03-30 22:02:32 +09:00
prio_tree.c
quicklist.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
readahead.c readahead: fix NULL filp dereference 2010-04-07 08:38:03 -07:00
rmap.c mm: migration: avoid race between shift_arg_pages() and rmap_walk() during migration by not migrating temporary stacks 2010-05-25 08:06:59 -07:00
shmem.c shmem: remove redundant code 2010-05-25 08:06:57 -07:00
slab.c cpuset,mm: fix no node to alloc memory when changing cpuset's mems 2010-05-25 08:06:57 -07:00
slob.c mm: Move ARCH_SLAB_MINALIGN and ARCH_KMALLOC_MINALIGN to <linux/slob_def.h> 2010-05-19 22:03:13 +03:00
slub.c cpuset,mm: fix no node to alloc memory when changing cpuset's mems 2010-05-25 08:06:57 -07:00
sparse-vmemmap.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
sparse.c sparsemem: on no vmemmap path put mem_map on node high too 2010-05-25 08:06:56 -07:00
swap.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
swap_state.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
swapfile.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging-2.6 2010-05-21 15:26:46 -07:00
thrash.c mm: pass mm to grab_swap_token 2009-06-23 12:50:05 -07:00
truncate.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
util.c slab: Generify kernel pointer validation 2010-04-09 10:09:50 -07:00
vmalloc.c mm: purge fragmented percpu vmap blocks 2010-02-02 12:50:47 -08:00
vmscan.c vmscan: prevent get_scan_ratio() rounding errors 2010-05-25 08:07:00 -07:00
vmstat.c mm: compaction: direct compact when a high-order allocation fails 2010-05-25 08:06:59 -07:00