On Tue, 11 Oct 2022 02:20:06 +0000 xu.xin.sc@xxxxxxxxx wrote: > From: xu xin <xu.xin16@xxxxxxxxxx> > > use_zero_pages is good, not just because of cache colouring as described > in doc, but also because use_zero_pages can accelerate merging empty pages > when there are plenty of empty pages (full of zeros) as the time of > page-by-page comparisons (unstable_tree_search_insert) is saved. > > But there is something to improve, that is, when enabling use_zero_pages, > all empty pages will be merged with kernel zero pages instead of with each > other as use_zero_pages is disabled, and then these zero-pages are no longer > managed and monitor by KSM, which leads to two issues at least: Sorry, but I'm struggling to understand what real value this patchset offers. > 1) MADV_UNMERGEABLE and other ways to trigger unsharing will *not* > unshare the shared zeropage as placed by KSM (which is against the > MADV_UNMERGEABLE documentation at least); see the link: > https://lore.kernel.org/lkml/4a3daba6-18f9-d252-697c-197f65578c44@xxxxxxxxxx/ Is that causing users any real-world problem? If not, just change the documentation? > 2) we cannot know how many pages are zero pages placed by KSM when > enabling use_zero_pages, which leads to KSM not being transparent > with all actual merged pages by KSM. Why is this a problem? A full description of the real-world end-user operational benefits of these changes would help, please.
