Now that ksm is in mainline it is better to change the default values to
better fit to most of the users.
This patch change the ksm default values to be:
ksm_thread_pages_to_scan = 100 (instead of 200)
ksm_thread_sleep_millisecs = 20 (like before)
ksm_run = KSM_RUN_STOP (instead of KSM_RUN_MERGE - meaning ksm is
disabled by default)
ksm_max_kernel_pages = nr_free_buffer_pages / 4 (instead of 2046)
The important aspect of this patch is: it disables ksm by default, and sets
the number of the kernel_pages that can be allocated to be a reasonable
number.
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
KSM is a linux driver that allows dynamicly sharing identical memory pages
between one or more processes.
Unlike tradtional page sharing that is made at the allocation of the
memory, ksm do it dynamicly after the memory was created. Memory is
periodically scanned; identical pages are identified and merged.
The sharing is made in a transparent way to the processes that use it.
Ksm is highly important for hypervisors (kvm), where in production
enviorments there might be many copys of the same data data among the host
memory. This kind of data can be: similar kernels, librarys, cache, and
so on.
Even that ksm was wrote for kvm, any userspace application that want to
use it to share its data can try it.
Ksm may be useful for any application that might have similar (page
aligment) data strctures among the memory, ksm will find this data merge
it to one copy, and even if it will be changed and thereforew copy on
writed, ksm will merge it again as soon as it will be identical again.
Another reason to consider using ksm is the fact that it might simplify
alot the userspace code of application that want to use shared private
data, instead that the application will mange shared area, ksm will do
this for the application, and even write to this data will be allowed
without any synchinization acts from the application.
Ksm was designed to be a loadable module that doesn't change the VM code
of linux.
This patch:
The set_pte_at_notify() macro allows setting a pte in the shadow page
table directly, instead of flushing the shadow page table entry and then
getting vmexit to set it. It uses a new change_pte() callback to do so.
set_pte_at_notify() is an optimization for kvm, and other users of
mmu_notifiers, for COW pages. It is useful for kvm when ksm is used,
because it allows kvm not to have to receive vmexit and only then map the
ksm page into the shadow page table, but instead map it directly at the
same time as Linux maps the page into the host page table.
Users of mmu_notifiers who don't implement new mmu_notifier_change_pte()
callback will just receive the mmu_notifier_invalidate_page() callback.
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
When slot is already allocated and being asked to be tracked we need
to break the large pages.
This code flush the mmu when someone ask a slot to start dirty bit
tracking.
Cc: stable@kernel.org
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
vmap() on guest pages hides those pages from the Linux mm for an extended
(userspace determined) amount of time. Get rid of it.
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit change the name of emulator_read_std into kvm_read_guest_virt,
and add new function name kvm_write_guest_virt that allow writing into a
guest virtual address.
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Some areas of kvm x86 mmu are using gfn offset inside a slot without
unaliasing the gfn first. This patch makes sure that the gfn will be
unaliased and add gfn_to_memslot_unaliased() to save the calculating
of the gfn unaliasing in case we have it unaliased already.
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Acked-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Izik Eidus