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The idea is that without doing more calculations we extend zero pages to same element pages for zram. zero page is special case of same element page with zero element. 1. the test is done under android 7.0 2. startup too many applications circularly 3. sample the zero pages, same pages (none-zero element) and total pages in function page_zero_filled the result is listed as below: ZERO SAME TOTAL 36214 17842 598196 ZERO/TOTAL SAME/TOTAL (ZERO+SAME)/TOTAL ZERO/SAME AVERAGE 0.060631909 0.024990816 0.085622726 2.663825038 STDEV 0.00674612 0.005887625 0.009707034 2.115881328 MAX 0.069698422 0.030046087 0.094975336 7.56043956 MIN 0.03959586 0.007332205 0.056055193 1.928985507 from the above data, the benefit is about 2.5% and up to 3% of total swapout pages. The defect of the patch is that when we recovery a page from non-zero element the operations are low efficient for partial read. This patch extends zero_page to same_page so if there is any user to have monitored zero_pages, he will be surprised if the number is increased but it's not harmful, I believe. [minchan@kernel.org: do not free same element pages in zram_meta_free] Link: http://lkml.kernel.org/r/20170207065741.GA2567@bbox Link: http://lkml.kernel.org/r/1483692145-75357-1-git-send-email-zhouxianrong@huawei.com Link: http://lkml.kernel.org/r/1486307804-27903-1-git-send-email-minchan@kernel.org Signed-off-by: zhouxianrong <zhouxianrong@huawei.com> Signed-off-by: Minchan Kim <minchan@kernel.org> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
123 lines
3.3 KiB
C
123 lines
3.3 KiB
C
/*
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* Compressed RAM block device
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*
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* Copyright (C) 2008, 2009, 2010 Nitin Gupta
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* 2012, 2013 Minchan Kim
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*
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* This code is released using a dual license strategy: BSD/GPL
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* You can choose the licence that better fits your requirements.
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*
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* Released under the terms of 3-clause BSD License
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* Released under the terms of GNU General Public License Version 2.0
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*
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*/
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#ifndef _ZRAM_DRV_H_
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#define _ZRAM_DRV_H_
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#include <linux/rwsem.h>
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#include <linux/zsmalloc.h>
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#include <linux/crypto.h>
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#include "zcomp.h"
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/*-- Configurable parameters */
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/*
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* Pages that compress to size greater than this are stored
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* uncompressed in memory.
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*/
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static const size_t max_zpage_size = PAGE_SIZE / 4 * 3;
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/*
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* NOTE: max_zpage_size must be less than or equal to:
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* ZS_MAX_ALLOC_SIZE. Otherwise, zs_malloc() would
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* always return failure.
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*/
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/*-- End of configurable params */
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#define SECTOR_SHIFT 9
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#define SECTORS_PER_PAGE_SHIFT (PAGE_SHIFT - SECTOR_SHIFT)
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#define SECTORS_PER_PAGE (1 << SECTORS_PER_PAGE_SHIFT)
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#define ZRAM_LOGICAL_BLOCK_SHIFT 12
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#define ZRAM_LOGICAL_BLOCK_SIZE (1 << ZRAM_LOGICAL_BLOCK_SHIFT)
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#define ZRAM_SECTOR_PER_LOGICAL_BLOCK \
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(1 << (ZRAM_LOGICAL_BLOCK_SHIFT - SECTOR_SHIFT))
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/*
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* The lower ZRAM_FLAG_SHIFT bits of table.value is for
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* object size (excluding header), the higher bits is for
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* zram_pageflags.
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*
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* zram is mainly used for memory efficiency so we want to keep memory
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* footprint small so we can squeeze size and flags into a field.
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* The lower ZRAM_FLAG_SHIFT bits is for object size (excluding header),
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* the higher bits is for zram_pageflags.
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*/
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#define ZRAM_FLAG_SHIFT 24
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/* Flags for zram pages (table[page_no].value) */
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enum zram_pageflags {
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/* Page consists entirely of zeros */
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ZRAM_SAME = ZRAM_FLAG_SHIFT,
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ZRAM_ACCESS, /* page is now accessed */
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__NR_ZRAM_PAGEFLAGS,
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};
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/*-- Data structures */
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/* Allocated for each disk page */
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struct zram_table_entry {
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union {
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unsigned long handle;
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unsigned long element;
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};
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unsigned long value;
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};
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struct zram_stats {
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atomic64_t compr_data_size; /* compressed size of pages stored */
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atomic64_t num_reads; /* failed + successful */
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atomic64_t num_writes; /* --do-- */
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atomic64_t failed_reads; /* can happen when memory is too low */
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atomic64_t failed_writes; /* can happen when memory is too low */
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atomic64_t invalid_io; /* non-page-aligned I/O requests */
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atomic64_t notify_free; /* no. of swap slot free notifications */
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atomic64_t same_pages; /* no. of same element filled pages */
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atomic64_t pages_stored; /* no. of pages currently stored */
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atomic_long_t max_used_pages; /* no. of maximum pages stored */
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atomic64_t writestall; /* no. of write slow paths */
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};
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struct zram_meta {
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struct zram_table_entry *table;
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struct zs_pool *mem_pool;
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};
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struct zram {
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struct zram_meta *meta;
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struct zcomp *comp;
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struct gendisk *disk;
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/* Prevent concurrent execution of device init */
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struct rw_semaphore init_lock;
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/*
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* the number of pages zram can consume for storing compressed data
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*/
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unsigned long limit_pages;
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struct zram_stats stats;
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/*
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* This is the limit on amount of *uncompressed* worth of data
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* we can store in a disk.
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*/
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u64 disksize; /* bytes */
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char compressor[CRYPTO_MAX_ALG_NAME];
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/*
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* zram is claimed so open request will be failed
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*/
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bool claim; /* Protected by bdev->bd_mutex */
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};
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#endif
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