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a85f878b44
Zswap is a cache which compresses the pages that are being swapped out
and stores them into a dynamically allocated RAM-based memory pool.
Experiments have shown that around 10-20% of pages stored in zswap are
same-filled pages (i.e. contents of the page are all same), but these
pages are handled as normal pages by compressing and allocating memory
in the pool.
This patch adds a check in zswap_frontswap_store() to identify
same-filled page before compression of the page. If the page is a
same-filled page, set zswap_entry.length to zero, save the same-filled
value and skip the compression of the page and alloction of memory in
zpool. In zswap_frontswap_load(), check if value of zswap_entry.length
is zero corresponding to the page to be loaded. If zswap_entry.length
is zero, fill the page with same-filled value. This saves the
decompression time during load.
On a ARM Quad Core 32-bit device with 1.5GB RAM by launching and
relaunching different applications, out of ~64000 pages stored in zswap,
~11000 pages were same-value filled pages (including zero-filled pages)
and ~9000 pages were zero-filled pages.
An average of 17% of pages(including zero-filled pages) in zswap are
same-value filled pages and 14% pages are zero-filled pages. An average
of 3% of pages are same-filled non-zero pages.
The below table shows the execution time profiling with the patch.
Baseline With patch % Improvement
-----------------------------------------------------------------
*Zswap Store Time 26.5ms 18ms 32%
(of same value pages)
*Zswap Load Time
(of same value pages) 25.5ms 13ms 49%
-----------------------------------------------------------------
On Ubuntu PC with 2GB RAM, while executing kernel build and other test
scripts and running multimedia applications, out of 360000 pages stored
in zswap 78000(~22%) of pages were found to be same-value filled pages
(including zero-filled pages) and 64000(~17%) are zero-filled pages. So
an average of %5 of pages are same-filled non-zero pages.
The below table shows the execution time profiling with the patch.
Baseline With patch % Improvement
-----------------------------------------------------------------
*Zswap Store Time 91ms 74ms 19%
(of same value pages)
*Zswap Load Time 50ms 7.5ms 85%
(of same value pages)
-----------------------------------------------------------------
*The execution times may vary with test device used.
Dan said:
: I did test this patch out this week, and I added some instrumentation to
: check the performance impact, and tested with a small program to try to
: check the best and worst cases.
:
: When doing a lot of swap where all (or almost all) pages are same-value, I
: found this patch does save both time and space, significantly. The exact
: improvement in time and space depends on which compressor is being used,
: but roughly agrees with the numbers you listed.
:
: In the worst case situation, where all (or almost all) pages have the
: same-value *except* the final long (meaning, zswap will check each long on
: the entire page but then still have to pass the page to the compressor),
: the same-value check is around 10-15% of the total time spent in
: zswap_frontswap_store(). That's a not-insignificant amount of time, but
: it's not huge. Considering that most systems will probably be swapping
: pages that aren't similar to the worst case (although I don't have any
: data to know that), I'd say the improvement is worth the possible
: worst-case performance impact.
[srividya.dr@samsung.com: add memset_l instead of for loop]
Link: http://lkml.kernel.org/r/20171018104832epcms5p1b2232e2236258de3d03d1344dde9fce0@epcms5p1
Signed-off-by: Srividya Desireddy <srividya.dr@samsung.com>
Acked-by: Dan Streetman <ddstreet@ieee.org>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Dinakar Reddy Pathireddy <dinakar.p@samsung.com>
Cc: SHARAN ALLUR <sharan.allur@samsung.com>
Cc: RAJIB BASU <rajib.basu@samsung.com>
Cc: JUHUN KIM <juhunkim@samsung.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Timofey Titovets <nefelim4ag@gmail.com>
Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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| .. | ||
| kasan | ||
| backing-dev.c | ||
| balloon_compaction.c | ||
| bootmem.c | ||
| cleancache.c | ||
| cma_debug.c | ||
| cma.c | ||
| cma.h | ||
| compaction.c | ||
| debug_page_ref.c | ||
| debug.c | ||
| dmapool.c | ||
| early_ioremap.c | ||
| fadvise.c | ||
| failslab.c | ||
| filemap.c | ||
| frame_vector.c | ||
| frontswap.c | ||
| gup_benchmark.c | ||
| gup.c | ||
| highmem.c | ||
| hmm.c | ||
| huge_memory.c | ||
| hugetlb_cgroup.c | ||
| hugetlb.c | ||
| hwpoison-inject.c | ||
| init-mm.c | ||
| internal.h | ||
| interval_tree.c | ||
| Kconfig | ||
| Kconfig.debug | ||
| khugepaged.c | ||
| kmemleak-test.c | ||
| kmemleak.c | ||
| ksm.c | ||
| list_lru.c | ||
| maccess.c | ||
| madvise.c | ||
| Makefile | ||
| memblock.c | ||
| memcontrol.c | ||
| memory_hotplug.c | ||
| memory-failure.c | ||
| memory.c | ||
| mempolicy.c | ||
| mempool.c | ||
| memtest.c | ||
| migrate.c | ||
| mincore.c | ||
| mlock.c | ||
| mm_init.c | ||
| mmap.c | ||
| mmu_context.c | ||
| mmu_notifier.c | ||
| mmzone.c | ||
| mprotect.c | ||
| mremap.c | ||
| msync.c | ||
| nobootmem.c | ||
| nommu.c | ||
| oom_kill.c | ||
| page_alloc.c | ||
| page_counter.c | ||
| page_ext.c | ||
| page_idle.c | ||
| page_io.c | ||
| page_isolation.c | ||
| page_owner.c | ||
| page_poison.c | ||
| page_vma_mapped.c | ||
| page-writeback.c | ||
| pagewalk.c | ||
| percpu-internal.h | ||
| percpu-km.c | ||
| percpu-stats.c | ||
| percpu-vm.c | ||
| percpu.c | ||
| pgtable-generic.c | ||
| process_vm_access.c | ||
| quicklist.c | ||
| readahead.c | ||
| rmap.c | ||
| rodata_test.c | ||
| shmem.c | ||
| slab_common.c | ||
| slab.c | ||
| slab.h | ||
| slob.c | ||
| slub.c | ||
| sparse-vmemmap.c | ||
| sparse.c | ||
| swap_cgroup.c | ||
| swap_slots.c | ||
| swap_state.c | ||
| swap.c | ||
| swapfile.c | ||
| truncate.c | ||
| usercopy.c | ||
| userfaultfd.c | ||
| util.c | ||
| vmacache.c | ||
| vmalloc.c | ||
| vmpressure.c | ||
| vmscan.c | ||
| vmstat.c | ||
| workingset.c | ||
| z3fold.c | ||
| zbud.c | ||
| zpool.c | ||
| zsmalloc.c | ||
| zswap.c | ||