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c0265342bf
zRam as swap is useful for small memory device. However, swap means
those pages on zram are mostly cold pages due to VM's LRU algorithm.
Especially, once init data for application are touched for launching,
they tend to be not accessed any more and finally swapped out. zRAM can
store such cold pages as compressed form but it's pointless to keep in
memory. Better idea is app developers free them directly rather than
remaining them on heap.
This patch tell us last access time of each block of zram via "cat
/sys/kernel/debug/zram/zram0/block_state".
The output is as follows,
300 75.033841 .wh
301 63.806904 s..
302 63.806919 ..h
First column is zram's block index and 3rh one represents symbol (s:
same page w: written page to backing store h: huge page) of the block
state. Second column represents usec time unit of the block was last
accessed. So above example means the 300th block is accessed at
75.033851 second and it was huge so it was written to the backing store.
Admin can leverage this information to catch cold|incompressible pages
of process with *pagemap* once part of heaps are swapped out.
I used the feature a few years ago to find memory hoggers in userspace
to notify them what memory they have wasted without touch for a long
time. With it, they could reduce unnecessary memory space. However, at
that time, I hacked up zram for the feature but now I need the feature
again so I decided it would be better to upstream rather than keeping it
alone. I hope I submit the userspace tool to use the feature soon.
[akpm@linux-foundation.org: fix i386 printk warning]
[minchan@kernel.org: use ktime_get_boottime() instead of sched_clock()]
Link: http://lkml.kernel.org/r/20180420063525.GA253739@rodete-desktop-imager.corp.google.com
[akpm@linux-foundation.org: documentation tweak]
[akpm@linux-foundation.org: fix i386 printk warning]
[minchan@kernel.org: fix compile warning]
Link: http://lkml.kernel.org/r/20180508104849.GA8209@rodete-desktop-imager.corp.google.com
[rdunlap@infradead.org: fix printk formats]
Link: http://lkml.kernel.org/r/3652ccb1-96ef-0b0b-05d1-f661d7733dcc@infradead.org
Link: http://lkml.kernel.org/r/20180416090946.63057-5-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
120 lines
3.3 KiB
C
120 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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#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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/* zram slot is locked */
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ZRAM_LOCK = ZRAM_FLAG_SHIFT,
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ZRAM_SAME, /* Page consists the same element */
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ZRAM_WB, /* page is stored on backing_device */
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ZRAM_HUGE, /* Incompressible page */
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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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#ifdef CONFIG_ZRAM_MEMORY_TRACKING
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ktime_t ac_time;
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#endif
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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 huge_pages; /* no. of huge 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 {
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struct zram_table_entry *table;
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struct zs_pool *mem_pool;
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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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#ifdef CONFIG_ZRAM_WRITEBACK
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struct file *backing_dev;
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struct block_device *bdev;
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unsigned int old_block_size;
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unsigned long *bitmap;
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unsigned long nr_pages;
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spinlock_t bitmap_lock;
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#endif
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#ifdef CONFIG_ZRAM_MEMORY_TRACKING
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struct dentry *debugfs_dir;
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#endif
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};
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#endif
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