- 22 9月, 2009 2 次提交
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由 Izik Eidus 提交于
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: NIzik Eidus <ieidus@redhat.com> Signed-off-by: NHugh Dickins <hugh.dickins@tiscali.co.uk> Signed-off-by: NChris 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: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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由 Hugh Dickins 提交于
This patch presents the mm interface to a dummy version of ksm.c, for better scrutiny of that interface: the real ksm.c follows later. When CONFIG_KSM is not set, madvise(2) reject MADV_MERGEABLE and MADV_UNMERGEABLE with EINVAL, since that seems more helpful than pretending that they can be serviced. But when CONFIG_KSM=y, accept them even if KSM is not currently running, and even on areas which KSM will not touch (e.g. hugetlb or shared file or special driver mappings). Like other madvices, report ENOMEM despite success if any area in the range is unmapped, and use EAGAIN to report out of memory. Define vma flag VM_MERGEABLE to identify an area on which KSM may try merging pages: leave it to ksm_madvise() to decide whether to set it. Define mm flag MMF_VM_MERGEABLE to identify an mm which might contain VM_MERGEABLE areas, to minimize callouts when forking or exiting. Based upon earlier patches by Chris Wright and Izik Eidus. Signed-off-by: NHugh Dickins <hugh.dickins@tiscali.co.uk> Signed-off-by: NChris Wright <chrisw@redhat.com> Signed-off-by: NIzik Eidus <ieidus@redhat.com> Cc: Michael Kerrisk <mtk.manpages@gmail.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: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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