* [PATCH v7 0/6] ksm: support tracking KSM-placed zero-pages
@ 2023-04-13 5:46 yang.yang29
2023-04-17 8:03 ` David Hildenbrand
0 siblings, 1 reply; 2+ messages in thread
From: yang.yang29 @ 2023-04-13 5:46 UTC (permalink / raw)
To: akpm, david
Cc: imbrenda, linux-kernel, linux-mm, ran.xiaokai, xu.xin.sc,
xu.xin16, yang.yang29
From: xu xin <xu.xin16@zte.com.cn>
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@zte.com.cn/
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.
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
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.
xu xin (6):
ksm: support unsharing KSM-placed zero pages
ksm: count all zero pages placed by KSM
ksm: add ksm zero pages for each process
ksm: add documentation for ksm zero pages
ksm: update the calculation of KSM profit
selftest: add a testcase of ksm zero pages
Documentation/admin-guide/mm/ksm.rst | 26 +++++---
fs/proc/base.c | 3 +
include/linux/ksm.h | 27 ++++++++
include/linux/mm_types.h | 11 +++-
mm/Kconfig | 23 ++++++-
mm/ksm.c | 28 ++++++++-
mm/memory.c | 7 ++-
tools/testing/selftests/mm/ksm_functional_tests.c | 75 +++++++++++++++++++++++
8 files changed, 187 insertions(+), 13 deletions(-)
--
2.15.2
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH v7 0/6] ksm: support tracking KSM-placed zero-pages
2023-04-13 5:46 [PATCH v7 0/6] ksm: support tracking KSM-placed zero-pages yang.yang29
@ 2023-04-17 8:03 ` David Hildenbrand
0 siblings, 0 replies; 2+ messages in thread
From: David Hildenbrand @ 2023-04-17 8:03 UTC (permalink / raw)
To: yang.yang29, akpm
Cc: imbrenda, linux-kernel, linux-mm, ran.xiaokai, xu.xin.sc,
xu.xin16, Stefan Roesch
On 13.04.23 07:46, yang.yang29@zte.com.cn wrote:
> From: xu xin <xu.xin16@zte.com.cn>
>
> 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@zte.com.cn/
>
> 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@redhat.com
[2] https://lkml.kernel.org/r/20230413233115.1878303-1-shr@devkernel.io
--
Thanks,
David / dhildenb
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2023-04-17 8:03 ` David Hildenbrand
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