On 05.11.24 10:15, Barry Song wrote:
On Tue, Nov 5, 2024 at 9:23 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
On 05.11.24 04:40, Andrew Morton wrote:
On Mon, 4 Nov 2024 13:32:55 +0100 David Hildenbrand <david@xxxxxxxxxx> wrote:
As mentioned above, this isn't about fixing a bug; it's simply to ensure
that swap-related metrics don't disappear.
Documentation/process/submitting-patches.rst:
"A Fixes: tag indicates that the patch fixes an issue in a previous
commit. It is used to make it easy to determine where a bug originated,
which can help review a bug fix."
If there is no BUG, I'm afraid you are abusing that tag.
I think the abuse is reasonable. We have no Should-be-included-with:.
A "Belongs-to:" might make sense, for this kind of stuff that is still
only in an RFC. Or we update the doc to explicitly spell out this
special case of using "Fixes" to sort out something into the RC.
Because if this would be already in a released kernel, it would get a
bit trickier: stable rules explicitly spell out "fix a real bug".
0ca0c24e3211 is only in 6.12-rcX so this is the time to make
userspace-visible tweaks, so the 6.12 interfaces are the same as the
6.13+ interfaces (which is what I think is happening here?)
> > And including the Fixes in this patch might be useful to someone who is
backporting 0ca0c24e3211 into some earlier kernel for their own
purposes.
Just to be clear: adding new counters would hardly be fixing existing
tools that perform calculations based on existing counters. So we are
already changing the "userspace-visible" portion in some way, and I have
no idea what in vmstat we consider "stable".
But I still don't think it's all that big of a deal except in some
handcrafted scenarios hardly anybody cares about; the cover letter is
also pretty clear on that.
I may have been mistaken in the cover letter. According to the zswap data Usama
provided for servers, zero-filled pages accounted for about 1%. So
really doesn't
matter too much, but I just checked with Hailong from our team—he has data
on same-page-filled usage in Android apps, which on average show 3-4%
same-page-filled, with over 85% being zero-filled. Some apps even reach
6-7% zero-filled pages. We previously used these counters to profile
optimizations, but with zeromap now serving as the frontend for swap files,
those counters will disappear entirely from both zRAM and pswpin/pswpout
metrics, as folios are filtered earlier.
Hailong essentially has a table that looks like the below which could be
collected from the existing counters:
com.xxx.app 5% same-page-filled. 88% zero
com.yyy.app 6% same-page-filled. 85% zero
com.zzz.map 6.7 same-page-filled. 88% zero
....
Anyone on 6.12 will be unable to track zero-filled pages unless they
backport this patch from a newer kernel version if it doesn’t make it
into 6.12.
Whether it's marked as 'Belongs-to:' or 'Fixes:', I'd prefer we aim to
land it in
6.12 :-)
Thanks for sharing these numbers. Just for the records, I think the
optimization is quite powerful. What I am not convinced is that the
missing stat is a big deal.
If I upgrade my car and it suddenly consumes 5% less fuel/energy I (a)
either won't notice at all or (b) am happy and don't care why; I won't
start digging through the updated manual, looking for some hidden gages
that might explain why :)
But I might be missing something important, and I do understand why it
can be helpful to have it black-on-white how much this optimization
gives you. So feel free to move forward with this as you like, having it
in 6.12 sounds very reasonable to me.
--
Cheers,
David / dhildenb
