On Mon, Oct 28, 2024 at 12:54 PM Barry Song <21cnbao@xxxxxxxxx> wrote: > > On Tue, Oct 29, 2024 at 1:20 AM Usama Arif <usamaarif642@xxxxxxxxx> wrote: > > > > > > > > On 28/10/2024 17:08, Yosry Ahmed wrote: > > > On Mon, Oct 28, 2024 at 10:00 AM Usama Arif <usamaarif642@xxxxxxxxx> wrote: > > >> > > >> > > >> > > >> On 28/10/2024 16:33, Nhat Pham wrote: > > >>> On Mon, Oct 28, 2024 at 5:23 AM Usama Arif <usamaarif642@xxxxxxxxx> wrote: > > >>>> > > >>>> I wonder if instead of having counters, it might be better to keep track > > >>>> of the number of zeropages currently stored in zeromap, similar to how > > >>>> zswap_same_filled_pages did it. It will be more complicated then this > > >>>> patch, but would give more insight of the current state of the system. > > >>>> > > >>>> Joshua (in CC) was going to have a look at that. > > >>> > > >>> I don't think one can substitute for the other. > > >> > > >> Yes agreed, they have separate uses and provide different information, but > > >> maybe wasteful to have both types of counters? They are counters so maybe > > >> dont consume too much resources but I think we should still think about > > >> it.. > > > > > > Not for or against here, but I would say that statement is debatable > > > at best for memcg stats :) > > > > > > Each new counter consumes 2 longs per-memcg per-CPU (see > > > memcg_vmstats_percpu), about 16 bytes, which is not a lot but it can > > > quickly add up with a large number of CPUs/memcgs/stats. > > > > > > Also, when flushing the stats we iterate all of them to propagate > > > updates from per-CPU counters. This is already a slowpath so adding > > > one stat is not a big deal, but again because we iterate all stats on > > > multiple CPUs (and sometimes on each node as well), the overall flush > > > latency becomes a concern sometimes. > > > > > > All of that is not to say we shouldn't add more memcg stats, but we > > > have to be mindful of the resources. > > > > Yes agreed! Plus the cost of incrementing similar counters (which ofcourse is > > also not much). > > > > Not trying to block this patch in anyway. Just think its a good point > > to discuss here if we are ok with both types of counters. If its too wasteful > > then which one we should have. > > Hi Usama, > my point is that with all the below three counters: > 1. PSWPIN/PSWPOUT > 2. ZSWPIN/ZSWPOUT > 3. SWAPIN_SKIP/SWAPOUT_SKIP or (ZEROSWPIN, ZEROSWPOUT what ever) > > Shouldn't we have been able to determine the portion of zeromap > swap indirectly? What about swap entries that get freed without being swapped in (e.g. swapped out anon memory freed, MADV_FREE, shmem truncate, etc)? > > Thanks > Barry
