mbox series

[v9,0/5] ksm: support tracking KSM-placed zero-pages

Message ID 202305241351365661923@zte.com.cn
Headers
Series ksm: support tracking KSM-placed zero-pages |

Message

Yang Yang May 24, 2023, 5:51 a.m. UTC 
  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.

Change log
----------
v8->v9:
------
(1) The previous [PATCH v8 4/6] is squashed into the current [PATCH v9 2/5].

(2) Improve the codes as David's suggestions.

v7->v8:
-------
(1) Since [1] which fix the bug of pte_mkdirty on sparc64 that makes pte
    writable, then we can remove the architechture restrictions of our
	features.
(2) Improve the scheme of update ksm_zero_pages: add the handling case when
    khugepaged replaces a shared zeropage by a THP. 

[1] https://lore.kernel.org/all/20230411141529.428991-2-david@redhat.com/

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 (5):
  ksm: support unsharing KSM-placed zero pages
  ksm: count all zero pages placed by KSM
  ksm: add ksm zero pages for each process
  ksm: consider KSM-placed zeropages when calculating KSM profit
  selftest: add a testcase of ksm zero pages

 Documentation/admin-guide/mm/ksm.rst              | 25 ++++++--
 fs/proc/base.c                                    |  1 +
 include/linux/ksm.h                               | 22 +++++++
 include/linux/mm_types.h                          |  9 ++-
 mm/khugepaged.c                                   |  2 +
 mm/ksm.c                                          | 28 ++++++--
 mm/memory.c                                       |  5 +-
 tools/testing/selftests/mm/ksm_functional_tests.c | 78 ++++++++++++++++++++++-
 8 files changed, 154 insertions(+), 16 deletions(-)

Comments

David Hildenbrand May 24, 2023, 9:12 a.m. UTC | #1 
On 24.05.23 07:51, 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.
> 


Ran the tests and they worked as expected. I only had some remaining 
feedback for the last patch, otherwise LGTM.