On Thu, Apr 28, 2022 at 7:36 AM Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > On Wed, Apr 27, 2022 at 04:36:22PM -0700, Shakeel Butt wrote: > > On Wed, Apr 27, 2022 at 3:32 PM Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > > > > > On Wed, Apr 27, 2022 at 05:20:31PM -0400, Johannes Weiner wrote: > > > > On Wed, Apr 27, 2022 at 01:29:34PM -0700, Minchan Kim wrote: > > > > > Hi Johannes, > > > > > > > > > > On Wed, Apr 27, 2022 at 12:00:15PM -0400, Johannes Weiner wrote: > > > > > > Currently it requires poking at debugfs to figure out the size and > > > > > > population of the zswap cache on a host. There are no counters for > > > > > > reads and writes against the cache. As a result, it's difficult to > > > > > > understand zswap behavior on production systems. > > > > > > > > > > > > Print zswap memory consumption and how many pages are zswapped out in > > > > > > /proc/meminfo. Count zswapouts and zswapins in /proc/vmstat. > > > > > > > > > > > > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> > > > > > > --- > > > > > > fs/proc/meminfo.c | 7 +++++++ > > > > > > include/linux/swap.h | 5 +++++ > > > > > > include/linux/vm_event_item.h | 4 ++++ > > > > > > mm/vmstat.c | 4 ++++ > > > > > > mm/zswap.c | 13 ++++++------- > > > > > > 5 files changed, 26 insertions(+), 7 deletions(-) > > > > > > > > > > > > diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c > > > > > > index 6fa761c9cc78..6e89f0e2fd20 100644 > > > > > > --- a/fs/proc/meminfo.c > > > > > > +++ b/fs/proc/meminfo.c > > > > > > @@ -86,6 +86,13 @@ static int meminfo_proc_show(struct seq_file *m, void *v) > > > > > > > > > > > > show_val_kb(m, "SwapTotal: ", i.totalswap); > > > > > > show_val_kb(m, "SwapFree: ", i.freeswap); > > > > > > +#ifdef CONFIG_ZSWAP > > > > > > + seq_printf(m, "Zswap: %8lu kB\n", > > > > > > + (unsigned long)(zswap_pool_total_size >> 10)); > > > > > > + seq_printf(m, "Zswapped: %8lu kB\n", > > > > > > + (unsigned long)atomic_read(&zswap_stored_pages) << > > > > > > + (PAGE_SHIFT - 10)); > > > > > > +#endif > > > > > > > > > > I agree it would be very handy to have the memory consumption in meminfo > > > > > > > > > > https://lore.kernel.org/all/YYwZXrL3Fu8%2FvLZw@xxxxxxxxxx/ > > > > > > > > > > If we really go this Zswap only metric instead of general term > > > > > "Compressed", I'd like to post maybe "Zram:" with same reason > > > > > in this patchset. Do you think that's better idea instead of > > > > > introducing general term like "Compressed:" or something else? > > > > > > > > I'm fine with changing it to Compressed. If somebody cares about a > > > > more detailed breakdown, we can add Zswap, Zram subsets as needed. > > > > > > It does raise the question what to do about cgroup, though. Should the > > > control files (memory.zswap.current & memory.zswap.max) apply to zram > > > in the future? If so, we should rename them, too. > > > > > > I'm not too familiar with zram, maybe you can provide some > > > background. AFAIU, Google uses zram quite widely; all the more > > > confusing why there is no container support for it yet. > > > > > > Could you shed some light? > > > > > > > I can shed light on the datacenter workloads. We use cgroup (still on > > v1) and zswap. For the workloads/applications, the swap (or zswap) is > > transparent in the sense that they are charged exactly the same > > irrespective of how much their memory is zswapped-out. Basically the > > applications see the same usage which is actually v1's > > memsw.usage_in_bytes. We dynamically increase the swap size if it is > > low, so we are not really worried about one job hogging the swap > > space. > > > > Regarding stats we actually do have them internally representing > > compressed size and number of pages in zswap. The compressed size is > > actually used for OOM victim selection. The memsw or v2's swap usage > > in the presence of compression based swap does not actually tell how > > much memory can potentially be released by evicting a job. For example > > if there are two jobs 'A' and 'B'. Both of them have 100 pages > > compressed but A's 100 pages are compressed to let's say 10 pages > > while B's 100 pages are compressed to 70 pages. It is preferable to > > kill B as that will release 70 pages. (This is a very simplified > > explanation of what we actually do). > > Ah, so zram is really only used by the mobile stuff after all. > > In the DC, I guess you don't use disk swap in conjunction with zswap, > so those writeback cache controls are less interesting to you? Yes, we have some modifications to zswap to make it work without any backing real swap. Though there is a future plan to move to zram eventually. > > But it sounds like you would benefit from the zswap(ped) counters in > memory.stat at least. Yes and I think if we need zram specific counters/stats in future, those can be added then. > > Thanks, that is enlightening!
