Re: [PATCH] fs/proc/task_mmu: count KSM-placed zero pages in smaps

[Jinjiang Tu <tujinjiang@huawei.com>]

在 2026/7/6 21:40, David Hildenbrand (Arm) 写道:
> On 7/6/26 14:13, Jinjiang Tu wrote:
>> When KSM deduplicates a page to the kernel zero page (i.e. when
>> /sys/kernel/mm/ksm/use_zero_pages=1), it places a zero PTE with the dirty
>> bit set. vm_normal_page() returns NULL for such PTEs, so smaps_pte_entry()
>> bails out before reaching smaps_account() and these pages are never counted
>> into mss->ksm. As a result /proc/<pid>/smaps and smaps_rollup report a KSM
>> value of 0 even though the region is fully merged.
>>
>> Count KSM-placed zero pages directly in smaps_pte_entry() using
>> is_ksm_zero_pte().
> Hm.
>
> We do expose "ksm_zero_pages" in /proc/<pid>/ksm_stat for calculating the KSM
> profit.
>
> Why would we want to expose it here as KSM pages?

I wasanalyzing the KSM profit of a process comes from which VMAs. However, 
smaps does not include the savings from ksm_zero_pages, make me fail to 
analyze.

> An application will notice the difference between "zeropage enabled vs.
> disabled" either way because we'll also not account zerpages towards e.g.,
> "Anonymous".
>
> So faking that something consumes memory when it actually doesn't consume memory
> is wrong?