On 8/24/22 19:48, xu xin wrote: > +Monitoring KSM profit > +===================== > + > +KSM can save memory by merging identical pages, but also can consume > +additional memory, because it needs to generate a number of rmap_items to > +save each scanned page's brief rmap information. Some of these pages may > +be merged, but some may not be abled to be merged after being checked > +several times, which are unprofitable memory consumed. > + > +1) How to determine whether KSM save memory or consume memory in system-wide > + range? Here is a simple approximate calculation for reference:: > + > + general_profit =~ pages_sharing * sizeof(page) - (all_rmap_items) * > + sizeof(rmap_item); > + > + where all_rmap_items can be easily obtained by summing ``pages_sharing``, > + ``pages_shared``, ``pages_unshared`` and ``pages_volatile``. > + > +2) The KSM profit inner a single process can be similarly obtained by the > + following approximate calculation:: > + > + process_profit =~ ksm_merging_pages * sizeof(page) - > + ksm_rmp_items * sizeof(rmap_item). > + > + where both ksm_merging_pages and ksm_rmp_items are shown under the > + directory ``/proc/<pid>/``. > + > +From the perspective of application, a high ratio of ``ksm_rmp_items`` to > +``ksm_merging_pages`` means a bad madvise-applied policy, so developers or > +administrators have to rethink how to change madvise policy. Giving an example > +for reference, a page's size is usually 4K, and the rmap_item's size is > +separately 32B on 32-bit CPU architecture and 64B on 64-bit CPU architecture. > +so if the ``ksm_rmp_items/ksm_merging_pages`` ratio exceeds 64 on 64-bit CPU > +or exceeds 128 on 32-bit CPU, then the app's madvise policy should be dropped, > +because the ksm profit is approximately zero or negative. > + > Monitoring KSM events > ===================== > LGTM. Reviewed-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx> -- An old man doll... just what I always wanted! - Clara
