On Thu, Apr 28, 2022 at 10:05:13AM -0400, Johannes Weiner wrote: > On Wed, Apr 27, 2022 at 03:12:17PM -0700, Minchan Kim wrote: > > On Wed, Apr 27, 2022 at 05:36:26PM -0400, Johannes Weiner 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. > > > > My usecase with zram is Android which doesn't use memcg. > > Ok. > > After more thought, my take is that in the future it could make sense > to track zram pages in a cgroup's memory.current. But it should NOT be > included in the dedicated memory.zswap.* files. Zswap is an in-kernel > writeback cache, and those files allow userspace to tune writeback > thresholds depending on the composition of the workload's > workingset. This doesn't translate to zram: the wb facility that it > has is triggered by hand, based on criteria such as idle pages and > compression rate. It's not based on size. From a cgroup POV, it's a > memory consumer that should be subject to memory.max, nothing more. > > This distinction applies to meminfo as well, though. While I think it > makes sense to have a combined "Compressed" counter for zram and > zswap, it's still important to understand zswap behavior on its own to > tune the system-wide writeback threshold in max_pool_percent. (And > again, while zram can also be limited, it's not a writeback threshold, > it's just a red line for returning -ENOMEM). > > So I'm going to keep the Zswap and Zswapped items and retract the > delta patch for renaming it to Compressed. > > But I'd ack a patch that adds a combined "Compressed" counter for zram > + zswap if you send it, Minchan. If we really want to go separate stat for zswap and zram, it would be better to use direct name "Zram: " instead of comrpessed.
