On 13.04.23 07:46, yang.yang29@xxxxxxxxxx wrote:
From: xu xin <xu.xin16@xxxxxxxxxx>
The core idea of this patch set is to enable users to perceive the number
of any pages merged by KSM, regardless of whether use_zero_page switch has
been turned on, so that users can know how much free memory increase is
really due to their madvise(MERGEABLE) actions. But the problem 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 monitored by KSM.
The motivations to do this is seen at:
https://lore.kernel.org/lkml/202302100915227721315@xxxxxxxxxx/
In one word, we hope to implement the support for KSM-placed zero pages
tracking without affecting the feature of use_zero_pages, so that app
developer can also benefit from knowing the actual KSM profit by getting
KSM-placed zero pages to optimize applications eventually when
/sys/kernel/mm/ksm/use_zero_pages is enabled.
Thanks for the update!
the patch uses pte_mkdirty (related with architecture) to mark KSM-placed
zero pages. Some architecture(like sparc64) treat R/O dirty PTEs as
writable, which will break KSM pages state (wrprotect) and affect
With [1] that should be resolved and we should be able to enable it
unconditionally.
Further, ideally this should get based on [2], such that we can include
the zeropages in the ksm and per-mm profit calculation.
Last but not least, I realized that we also have to handle the case when
khugepaged replaces a shared zeropage by a THP. I think that should be
easy by adjusting the counters in the the is_zero_pfn() handling in
mm/khugepaged.c:__collapse_huge_page_copy().
the KSM functionality. For safety, we restrict this feature only to the
tested and known-working architechtures (ARM, ARM64, and X86) fow now.
Change log
----------
v6->v7:
This is an all-newed version which is different from v6 which relys on KSM's
rmap_item. The patch series don't rely on rmap_item but pte_dirty, so the
general handling of tracking KSM-placed zero-pages is simplified a lot.
For safety, we restrict this feature only to the tested and known-working
architechtures (ARM, ARM64, and X86) fow now.
Yeah, with [1] this can be further simplified.
I'll be on vacation starting on Thursday for ~1.5 weeks, not sure if I
get to review before that. But it's unlikely that we'll make the
upcoming merge windows, so I guess we still have time (especially, for
[1] and [2] to land)
[1] https://lkml.kernel.org/r/20230411142512.438404-4-david@xxxxxxxxxx
[2] https://lkml.kernel.org/r/20230413233115.1878303-1-shr@xxxxxxxxxxxx
--
Thanks,
David / dhildenb
