Messages in this thread | | | Date | Fri, 13 Apr 2007 10:25:59 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH 0/13] maps: pagemap, kpagemap, and related cleanups |
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William Lee Irwin III wrote: > On Thu, 12 Apr 2007 16:10:50 -0700 William Lee Irwin III <wli@holomorphy.com> wrote: > >>>This solves a real-life problem for Oracle system monitoring software >>>(specifically EM). Among the tasks it must carry out is determining >>>per-process memory footprint of a set of cooperating tasks (i.e. Oracle >>>processes). RSS is inadequate for this due to page sharing; this work >>>provides sufficient information to determine what EM needs. > > > On Thu, Apr 12, 2007 at 04:32:35PM -0700, Andrew Morton wrote: > >>Not a good idea to expose raw flags in this manner - it changes at the drop >>of a hat. We'd need to also expose the kernel's PG_foo-to-bitnumber >>mapping to make this viable. >>Not a good idea to use page->_count: page_count() will be more stable. >>Otherwise OK, I guess: the interpretation of the page refcount is unlikely >>to change much over time. > > > EM wants to determine page_mapcount() for the most part for the > purposes of determining "uniquely attributable RSS" (my ca. 2004 > nomenclature) or "proportional RSS" (mpm's more recent nomenclature); > as things now stand it will have to infer them by maintaining a table > of pfn's and mappings thereof, but at least that can be done with it.
I don't know whether you can easily determine page_mapcount with page_count and flags, though (count gives you an educated guess, but mapcount is the real thing).
page_mapcount sounds very reasonable to export. It is directly tied with the userspace concept of mapping pages. page_count doesn't seem very useful (and if you must have it, please use page_count), neither does page flags.
You could have a bit indicating whether the page is free or not (but that doesn't tell you much that meminfo or zoneinfo or buddyinfo does not). Dirty/writeback/referenced/uptodate maybe?... I'm stumped, what's flags for?
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