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ec9516fbc5
linux/mm
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Hugh Dickins ec9516fbc5 tmpfs: optimize clearing when writing 
Nick proposed years ago that tmpfs should avoid clearing its pages where
write will overwrite them with new data, as ramfs has long done.  But I
messed it up and just got bad data.  Tried again recently, it works
fine.

Here's time output for writing 4GiB 16 times on this Core i5 laptop:

before: real	0m21.169s user	0m0.028s sys	0m21.057s
        real	0m21.382s user	0m0.016s sys	0m21.289s
        real	0m21.311s user	0m0.020s sys	0m21.217s

after:  real	0m18.273s user	0m0.032s sys	0m18.165s
        real	0m18.354s user	0m0.020s sys	0m18.265s
        real	0m18.440s user	0m0.032s sys	0m18.337s

ramfs:  real	0m16.860s user	0m0.028s sys	0m16.765s
        real	0m17.382s user	0m0.040s sys	0m17.273s
        real	0m17.133s user	0m0.044s sys	0m17.021s

Yes, I have done perf reports, but they need more explanation than they
deserve: in summary, clear_page vanishes, its cache loading shifts into
copy_user_generic_unrolled; shmem_getpage_gfp goes down, and
surprisingly mark_page_accessed goes way up - I think because they are
respectively where the cache gets to be reloaded after being purged by
clear or copy.

Suggested-by: Nick Piggin <npiggin@gmail.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-05-29 16:22:22 -07:00
..
backing-dev.c backing-dev: fix wakeup timer races with bdi_unregister() 2012-02-01 16:52:49 +08:00
bootmem.c mm: remove sparsemem allocation details from the bootmem allocator 2012-05-29 16:22:22 -07:00
bounce.c mm: remove the second argument of k[un]map_atomic() 2012-03-20 21:48:27 +08:00
cleancache.c mm: cleancache: Use __read_mostly as appropiate. 2012-01-23 16:08:09 -05:00
compaction.c mm: compaction: handle incorrect MIGRATE_UNMOVABLE type pageblocks 2012-05-29 16:22:22 -07:00
debug-pagealloc.c mm, x86: Remove debug_pagealloc_enabled 2011-12-06 09:24:07 +01:00
dmapool.c mm: fix implicit stat.h usage in dmapool.c 2011-10-31 09:20:12 -04:00
fadvise.c fadvise: only initiate writeback for specified range with FADV_DONTNEED 2012-01-10 16:30:43 -08:00
failslab.c switch debugfs to umode_t 2012-01-03 22:54:56 -05:00
filemap_xip.c mm/filemap_xip.c: fix race condition in xip_file_fault() 2012-02-03 16:16:41 -08:00
filemap.c radix-tree: use iterators in find_get_pages* functions 2012-03-28 17:14:37 -07:00
fremap.c mm: delete various needless include <linux/module.h> 2011-10-31 09:20:11 -04:00
highmem.c Merge branch 'modsplit-Oct31_2011' of git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux 2011-11-06 19:44:47 -08:00
huge_memory.c mm, thp: drop page_table_lock to uncharge memcg pages 2012-05-29 16:22:20 -07:00
hugetlb.c mm/hugetlb.c: use long vars instead of int in region_count() 2012-05-29 16:22:18 -07:00
hwpoison-inject.c HWPOISON: Clean up memory_failure() vs. __memory_failure() 2012-01-03 12:06:32 -08:00
init-mm.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
internal.h mm: compaction: handle incorrect MIGRATE_UNMOVABLE type pageblocks 2012-05-29 16:22:22 -07:00
Kconfig Cross Memory Attach: make it Kconfigurable 2012-05-29 16:22:20 -07:00
Kconfig.debug mm: more intensive memory corruption debugging 2012-01-10 16:30:42 -08:00
kmemcheck.c
kmemleak-test.c kmemleak: remove memset by using kzalloc 2011-01-27 18:31:51 +00:00
kmemleak.c kmemleak: Disable early logging when kmemleak is off by default 2012-01-20 16:57:05 +00:00
ksm.c ksm: cleanup: introduce find_mergeable_vma() 2012-03-21 17:54:59 -07:00
maccess.c mm: Map most files to use export.h instead of module.h 2011-10-31 09:20:12 -04:00
madvise.c coredump: add VM_NODUMP, MADV_NODUMP, MADV_CLEAR_NODUMP 2012-03-23 16:58:42 -07:00
Makefile Cross Memory Attach: make it Kconfigurable 2012-05-29 16:22:20 -07:00
memblock.c memblock: memblock should be able to handle zero length operations 2012-04-20 11:18:46 -07:00
memcontrol.c shmem: replace page if mapping excludes its zone 2012-05-29 16:22:22 -07:00
memory_hotplug.c mm: print physical addresses consistently with other parts of kernel 2012-05-29 16:22:21 -07:00
memory-failure.c mm/memory_failure: let the compiler add the function name 2012-05-29 16:22:18 -07:00
memory.c thp, memcg: split hugepage for memcg oom on cow 2012-05-29 16:22:19 -07:00
mempolicy.c mm: do_migrate_pages(): rename arguments 2012-05-29 16:22:20 -07:00
mempool.c mempool: fix first round failure behavior 2012-01-10 16:30:45 -08:00
migrate.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2012-05-23 17:42:39 -07:00
mincore.c mm: thp: fix pmd_bad() triggering in code paths holding mmap_sem read mode 2012-03-21 17:54:54 -07:00
mlock.c vm: avoid using find_vma_prev() unnecessarily 2012-03-06 18:23:36 -08:00
mm_init.c mm: Map most files to use export.h instead of module.h 2011-10-31 09:20:12 -04:00
mmap.c mm/mmap.c: find_vma(): remove unnecessary if(mm) check 2012-05-29 16:22:19 -07:00
mmu_context.c mm, counters: remove task argument to sync_mm_rss() and __sync_task_rss_stat() 2012-03-21 17:54:59 -07:00
mmu_notifier.c mm: Map most files to use export.h instead of module.h 2011-10-31 09:20:12 -04:00
mmzone.c mm: delete various needless include <linux/module.h> 2011-10-31 09:20:11 -04:00
mprotect.c Merge branch 'akpm' (Andrew's patch-bomb) 2012-03-22 09:04:48 -07:00
mremap.c mm: collapse security_vm_enough_memory() variants into a single function 2012-02-14 10:45:39 +11:00
msync.c
nobootmem.c mm: remove sparsemem allocation details from the bootmem allocator 2012-05-29 16:22:22 -07:00
nommu.c kill mm argument of vm_munmap() 2012-04-21 01:58:20 -04:00
oom_kill.c userns: Store uid and gid values in struct cred with kuid_t and kgid_t types 2012-05-03 03:28:38 -07:00
page_alloc.c mm: compaction: handle incorrect MIGRATE_UNMOVABLE type pageblocks 2012-05-29 16:22:22 -07:00
page_cgroup.c page_cgroup: fix horrid swap accounting regression 2012-03-06 08:18:23 -08:00
page_io.c block: kill off REQ_UNPLUG 2011-03-10 08:52:27 +01:00
page_isolation.c mm: page_isolation: MIGRATE_CMA isolation functions added 2012-05-21 15:09:33 +02:00
page-writeback.c writeback: initialize global_dirty_limit 2012-05-06 13:41:58 +08:00
pagewalk.c mm: thp: fix pmd_bad() triggering in code paths holding mmap_sem read mode 2012-03-21 17:54:54 -07:00
percpu-km.c percpu: clear memory allocated with the km allocator 2010-10-02 10:28:42 +03:00
percpu-vm.c percpu: use bitmap_clear 2012-01-20 09:23:16 -08:00
percpu.c kmemleak: Fix the kmemleak tracking of the percpu areas with !SMP 2012-05-09 10:13:29 -07:00
pgtable-generic.c arch/tile: allow building Linux with transparent huge pages enabled 2012-05-25 12:48:21 -04:00
prio_tree.c sanitize <linux/prefetch.h> usage 2011-05-20 12:50:29 -07:00
process_vm_access.c Fix race in process_vm_rw_core 2012-02-02 12:55:17 -08:00
quicklist.c mm: delete various needless include <linux/module.h> 2011-10-31 09:20:11 -04:00
readahead.c mm: Map most files to use export.h instead of module.h 2011-10-31 09:20:12 -04:00
rmap.c mm: remove swap token code 2012-05-29 16:22:19 -07:00
shmem.c tmpfs: optimize clearing when writing 2012-05-29 16:22:22 -07:00
slab.c Merge branch 'slab/for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/penberg/linux 2012-03-28 15:04:26 -07:00
slob.c mm: Map most files to use export.h instead of module.h 2011-10-31 09:20:12 -04:00
slub.c slub: missing test for partial pages flush work in flush_all() 2012-05-17 18:00:51 -07:00
sparse-vmemmap.c mm: delete various needless include <linux/module.h> 2011-10-31 09:20:11 -04:00
sparse.c mm: remove sparsemem allocation details from the bootmem allocator 2012-05-29 16:22:22 -07:00
swap_state.c mm: fix s390 BUG by __set_page_dirty_no_writeback on swap 2012-04-23 18:19:22 -07:00
swap.c mm: drain percpu lru add/rotate page-vectors on cpu hot-unplug 2012-03-21 17:54:58 -07:00
swapfile.c shmem: replace page if mapping excludes its zone 2012-05-29 16:22:22 -07:00
truncate.c mm for fs: add truncate_pagecache_range() 2012-03-28 17:14:35 -07:00
util.c procfs: mark thread stack correctly in proc/<pid>/maps 2012-03-21 17:54:58 -07:00
vmalloc.c mm: use kcalloc() instead of kzalloc() to allocate array 2012-05-29 16:22:19 -07:00
vmscan.c mm: rename is_mlocked_vma() to mlocked_vma_newpage() 2012-05-29 16:22:20 -07:00
vmstat.c mm/vmstat.c: remove debug fs entries on failure of file creation and made extfrag_debug_root dentry local 2012-05-29 16:22:19 -07:00