linux-kernel - [PATCH v2 0/5] ksm: support tracking KSM-placed zero-pages

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Date:   Sun,  9 Oct 2022 02:18:16 +0000
From:   xu.xin.sc@...il.com
To:     akpm@...ux-foundation.org
Cc:     ran.xiaokai@....com.cn, yang.yang29@....com.cn,
        jiang.xuexin@....com.cn, imbrenda@...ux.ibm.com, david@...hat.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        xu xin <xu.xin16@....com.cn>
Subject: [PATCH v2 0/5] ksm: support tracking KSM-placed zero-pages

From: xu xin <xu.xin16@....com.cn>

Before enabling use_zero_pages by setting /sys/kernel/mm/ksm/
use_zero_pages to 1, pages_sharing of KSM is basically accurate. But
when enabling use_zero_pages, all empty pages that are merged with
kernel zero page are not counted in pages_sharing or pages_shared.
That is because these empty pages are merged with zero-pages then no
longer managed by KSM, which leads to two issues at least:

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@redhat.com/

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.

With the patch series, we can unshare zero-pages(KSM-placed) accurately
and count ksm zero pages.

---
v1->v2:

[patch 4/5] fix build warning, mm/ksm.c:550, misleading indentation; statement 
'rmap_item->mm->ksm_zero_pages_sharing--;' is not part of the previous 'if'.

*** BLURB HERE ***

xu xin (5):
  ksm: abstract the function try_to_get_old_rmap_item
  ksm: support unsharing zero pages placed by KSM
  ksm: count all zero pages placed by KSM
  ksm: count zero pages for each process
  ksm: add zero_pages_sharing documentation

 Documentation/admin-guide/mm/ksm.rst |  10 +-
 fs/proc/base.c                       |   1 +
 include/linux/mm_types.h             |   7 +-
 mm/ksm.c                             | 177 +++++++++++++++++++++------
 4 files changed, 157 insertions(+), 38 deletions(-)

-- 
2.25.1