On 06.04.22 09:37, CGEL wrote:
> On Wed, Mar 23, 2022 at 09:49:46AM +0100, David Hildenbrand wrote:
>> On 22.03.22 12:04, cgel.zte@xxxxxxxxx wrote:
>>> From: Yang Yang <yang.yang29@xxxxxxxxxx>
>>>
>>> Delay accounting does not track the delay of COW. When tasks trigger
>>> much COW, it may spend a amount of time waiting for it. To get the
>>> impact of tasks in COW, measure the delay when it happens. This
>>> could help users to do tunnings, such as decide whether to use
>>> ksm or not.
>>>
>>> Also update tools/accounting/getdelays.c:
>>>
>>> / # ./getdelays -dl -p 231
>>> print delayacct stats ON
>>> listen forever
>>> PID 231
>>>
>>> CPU count real total virtual total delay total delay average
>>> 6247 1859000000 2154070021 1674255063 0.268ms
>>> IO count delay total delay average
>>> 0 0 0ms
>>> SWAP count delay total delay average
>>> 0 0 0ms
>>> RECLAIM count delay total delay average
>>> 0 0 0ms
>>> THRASHING count delay total delay average
>>> 0 0 0ms
>>> COMPACT count delay total delay average
>>> 3 72758 0ms
>>> COW count delay total delay average
>>> 3635 271567604 0ms
>>
>> You should also update Documentation/accounting/delay-accounting.rst
>> most probably.
>>
>> Overall LGTM and this might be of value not only for KSM but for anybody
>> using fork(). There will be collisions with [1], especially [2], which I
>> want to get in -next early after we have v5.18-rc1 (after rebasing [1]
>> on top of this).
>>
>> We'll have to decide if we want to also account hugetlb wp code
>> (hugetlb_cow), and if we want to account "unsharing" here as well under
>> cow (I tend to say that we want to for simplicity). For THP, we only
>> split and don't copy, so there isn't anything to account.
>>
> As for simplicity, what about account "PAGECOPY" instead of "COW"?
> "PAGECOPY" include COW and unsharing. And we may also account hugetlb
> wp in follow-up patches, based on this patch is sufficient reviewed.
PAGECOPY might be too generic. You actually want to express "potentially
shared page was copied by the write-fault handler while it was write
protected".
do_wp_page()->wp_page_copy()
Maybe simply "WP_COPY" as a prefix ("Write-protect copy") ?
--
Thanks,
David / dhildenb
