On 05/11/2024 09:15, 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%. 10% not 1% (https://lore.kernel.org/all/20240612124750.2220726-1-usamaarif642@xxxxxxxxx/). > 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. > This is what I meant in https://lore.kernel.org/all/79deed1a-9b0e-42e0-be2f-f0c3ef5fee11@xxxxxxxxx/ when I said it affects zram as well! I am happy with the current version of the patch, just need the change in Documentation/admin-guide/cgroup-v2.rst. Thanks, Usama > 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 :-) > >> >> So I'll shut up now and let people figure out the naming first, and if a >> new counter is required at all :) >> >> -- >> Cheers, >> >> David / dhildenb >> > > Thanks > Barry
