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33c3fc71c8
Knowing the portion of memory that is not used by a certain application or
memory cgroup (idle memory) can be useful for partitioning the system
efficiently, e.g. by setting memory cgroup limits appropriately.
Currently, the only means to estimate the amount of idle memory provided
by the kernel is /proc/PID/{clear_refs,smaps}: the user can clear the
access bit for all pages mapped to a particular process by writing 1 to
clear_refs, wait for some time, and then count smaps:Referenced. However,
this method has two serious shortcomings:
- it does not count unmapped file pages
- it affects the reclaimer logic
To overcome these drawbacks, this patch introduces two new page flags,
Idle and Young, and a new sysfs file, /sys/kernel/mm/page_idle/bitmap.
A page's Idle flag can only be set from userspace by setting bit in
/sys/kernel/mm/page_idle/bitmap at the offset corresponding to the page,
and it is cleared whenever the page is accessed either through page tables
(it is cleared in page_referenced() in this case) or using the read(2)
system call (mark_page_accessed()). Thus by setting the Idle flag for
pages of a particular workload, which can be found e.g. by reading
/proc/PID/pagemap, waiting for some time to let the workload access its
working set, and then reading the bitmap file, one can estimate the amount
of pages that are not used by the workload.
The Young page flag is used to avoid interference with the memory
reclaimer. A page's Young flag is set whenever the Access bit of a page
table entry pointing to the page is cleared by writing to the bitmap file.
If page_referenced() is called on a Young page, it will add 1 to its
return value, therefore concealing the fact that the Access bit was
cleared.
Note, since there is no room for extra page flags on 32 bit, this feature
uses extended page flags when compiled on 32 bit.
[akpm@linux-foundation.org: fix build]
[akpm@linux-foundation.org: kpageidle requires an MMU]
[akpm@linux-foundation.org: decouple from page-flags rework]
Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Greg Thelen <gthelen@google.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
43 lines
1.3 KiB
Plaintext
43 lines
1.3 KiB
Plaintext
00-INDEX
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- this file.
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active_mm.txt
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- An explanation from Linus about tsk->active_mm vs tsk->mm.
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balance
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- various information on memory balancing.
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cleancache.txt
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- Intro to cleancache and page-granularity victim cache.
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frontswap.txt
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- Outline frontswap, part of the transcendent memory frontend.
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highmem.txt
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- Outline of highmem and common issues.
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hugetlbpage.txt
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- a brief summary of hugetlbpage support in the Linux kernel.
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hwpoison.txt
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- explains what hwpoison is
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idle_page_tracking.txt
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- description of the idle page tracking feature.
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ksm.txt
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- how to use the Kernel Samepage Merging feature.
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numa
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- information about NUMA specific code in the Linux vm.
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numa_memory_policy.txt
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- documentation of concepts and APIs of the 2.6 memory policy support.
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overcommit-accounting
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- description of the Linux kernels overcommit handling modes.
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page_migration
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- description of page migration in NUMA systems.
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pagemap.txt
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- pagemap, from the userspace perspective
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slub.txt
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- a short users guide for SLUB.
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soft-dirty.txt
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- short explanation for soft-dirty PTEs
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split_page_table_lock
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- Separate per-table lock to improve scalability of the old page_table_lock.
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transhuge.txt
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- Transparent Hugepage Support, alternative way of using hugepages.
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unevictable-lru.txt
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- Unevictable LRU infrastructure
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zswap.txt
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- Intro to compressed cache for swap pages
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