admin-guide/mm/ksm.rst

18 which have been registered with it, looking for pages of identical
21 content). The amount of pages that KSM daemon scans in a single pass
25 KSM only merges anonymous (private) pages, never pagecache (file) pages.
26 KSM's merged pages were originally locked into kernel memory, but can now
27 be swapped out just like other user pages (but sharing is broken when they
45 to cancel that advice and restore unshared pages: whereupon KSM
55 cannot contain any pages which KSM could actually merge; even if
80         how many pages to scan before ksmd goes to sleep
95         specifies if pages from different NUMA nodes can be merged.
96         When set to 0, ksm merges only pages which physically reside
98         latency to access of shared pages. Systems with more nodes, at
105         when there are no ksm shared pages in the system: set run 2 to
106         unmerge pages first, then to 1 after changing
112         * set to 0 to stop ksmd from running but keep merged pages,
114         * set to 2 to stop ksmd and unmerge all pages currently merged, but
121         specifies whether empty pages (i.e. allocated pages that only
123         empty pages are merged with the kernel zero page(s) instead of
125         the performance on architectures with coloured zero pages,
128         KSM for some workloads, for example if the checksums of pages
131         effective for pages merged after the change.
154         specifies how frequently KSM checks the metadata of the pages
164         enabled, pages that have previously not been de-duplicated get
165         skipped. How often these pages are skipped depends on how often
183         pages. The default value is 200 seconds.
198         how many pages are being scanned for ksm
200         how many shared pages are being used
204         how many pages unique but repeatedly checked for merging
206         how many pages changing too fast to be placed in a tree
208         how many pages did the "smart" page scanning algorithm skip
212         the number of KSM pages that hit the ``max_page_sharing`` limit
214         number of duplicated KSM pages
216         how many zero pages that are still mapped into processes were mapped by
220 ``ksm_zero_pages`` represents the actual number of pages saved by KSM.
236 KSM can save memory by merging identical pages, but also can consume
238 save each scanned page's brief rmap information. Some of these pages may
295 The number of candidate pages for KSM is dynamic. It can be often observed
296 that during the startup of an application more candidate pages need to be
298 sized for the maximum number of candidate pages. The scan time advisor can
302 number of candidate pages to scan. Two advisors are implemented: none and
309 scan all the KSM candidate pages. The parameter ``advisor_target_scan_time``
310 decides how aggressive the scan time advisor scans candidate pages. Lower