qiurui
/
Centos-kernel-stream-9
mirror of https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

ksm: support unsharing KSM-placed zero pages 

JIRA: https://issues.redhat.com/browse/RHEL-27743

This patch is a backport of the following upstream commit:
commit 79271476b3362a9e69adae949a520647f8af3559
Author: xu xin <xu.xin16@zte.com.cn>
Date:   Tue Jun 13 11:09:28 2023 +0800

    ksm: support unsharing KSM-placed zero pages

    Patch series "ksm: support tracking KSM-placed zero-pages", v10.

    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.

    This patch (of 5):

    When use_zero_pages of ksm is enabled, madvise(addr, len,
    MADV_UNMERGEABLE) and other ways (like write 2 to /sys/kernel/mm/ksm/run)
    to trigger unsharing will *not* actually unshare the shared zeropage as
    placed by KSM (which is against the MADV_UNMERGEABLE documentation).  As
    these KSM-placed zero pages are out of the control of KSM, the related
    counts of ksm pages don't expose how many zero pages are placed by KSM
    (these special zero pages are different from those initially mapped zero
    pages, because the zero pages mapped to MADV_UNMERGEABLE areas are
    expected to be a complete and unshared page).

    To not blindly unshare all shared zero_pages in applicable VMAs, the patch
    use pte_mkdirty (related with architecture) to mark KSM-placed zero pages.
    Thus, MADV_UNMERGEABLE will only unshare those KSM-placed zero pages.

    In addition, we'll reuse this mechanism to reliably identify KSM-placed
    ZeroPages to properly account for them (e.g., calculating the KSM profit
    that includes zeropages) in the latter patches.

    The patch will not degrade the performance of use_zero_pages as it doesn't
    change the way of merging empty pages in use_zero_pages's feature.

    Link: https://lkml.kernel.org/r/202306131104554703428@zte.com.cn
    Link: https://lkml.kernel.org/r/20230613030928.185882-1-yang.yang29@zte.com.cn
    Signed-off-by: xu xin <xu.xin16@zte.com.cn>
    Acked-by: David Hildenbrand <david@redhat.com>
    Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
    Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn>
    Reviewed-by: Xiaokai Ran <ran.xiaokai@zte.com.cn>
    Reviewed-by: Yang Yang <yang.yang29@zte.com.cn>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Rafael Aquini <raquini@redhat.com>
This commit is contained in:
Rafael Aquini 2024-09-27 10:42:58 -04:00
parent 735e8fcedc
commit eb91b58bf5
2 changed files with 14 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/ksm.h
View File

@ -26,6 +26,12 @@ int ksm_disable(struct mm_struct *mm);
int __ksm_enter(struct mm_struct *mm);
void __ksm_exit(struct mm_struct *mm);
/*
* To identify zeropages that were mapped by KSM, we reuse the dirty bit
* in the PTE. If the PTE is dirty, the zeropage was mapped by KSM when
* deduplicating memory.
*/
#define is_ksm_zero_pte(pte) (is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte))
static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
{

11
mm/ksm.c
View File

@ -448,7 +448,8 @@ static int break_ksm_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long nex
if (is_migration_entry(entry))
page = pfn_swap_entry_to_page(entry);
}
ret = page && PageKsm(page);
/* return 1 if the page is an normal ksm page or KSM-placed zero page */
ret = (page && PageKsm(page)) || is_ksm_zero_pte(*pte);
pte_unmap_unlock(pte, ptl);
return ret;
}
@ -1229,8 +1230,12 @@ static int replace_page(struct vm_area_struct *vma, struct page *page,
page_add_anon_rmap(kpage, vma, addr, RMAP_NONE);
newpte = mk_pte(kpage, vma->vm_page_prot);
} else {
newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage),
vma->vm_page_prot));
/*
* Use pte_mkdirty to mark the zero page mapped by KSM, and then
* we can easily track all KSM-placed zero pages by checking if
* the dirty bit in zero page's PTE is set.
*/
newpte = pte_mkdirty(pte_mkspecial(pfn_pte(page_to_pfn(kpage), vma->vm_page_prot)));
/*
* We're replacing an anonymous page with a zero page, which is
* not anonymous. We need to do proper accounting otherwise we