On Thu, Apr 28, 2022 at 02:34:28PM -0400, Johannes Weiner wrote: > On Thu, Apr 28, 2022 at 10:31:45AM -0700, Minchan Kim wrote: > > On Thu, Apr 28, 2022 at 01:23:21PM -0400, Johannes Weiner wrote: > > > On Thu, Apr 28, 2022 at 09:59:53AM -0700, Minchan Kim wrote: > > > > On Thu, Apr 28, 2022 at 10:25:59AM -0400, Johannes Weiner wrote: > > > > > On Wed, Apr 27, 2022 at 03:16:48PM -0700, Minchan Kim wrote: > > > > > > On Wed, Apr 27, 2022 at 05:20:29PM -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. > > > > > > > > > > > > Thanks! Please consider ZSWPIN to rename more general term, too. > > > > > > > > > > That doesn't make sense to me. > > > > > > > > > > Zram is a swap backend, its traffic is accounted in PSWPIN/OUT. Zswap > > > > > is a writeback cache on top of the swap backend. It has pages > > > > > entering, refaulting, and being written back to the swap backend > > > > > (PSWPOUT). A zswpout and a zramout are different things. > > > > > > > > Think about that system has two swap devices (storage + zram). > > > > I think it's useful to know how many swap IO comes from zram > > > > and rest of them are storage. > > > > > > Hm, isn't this comparable to having one swap on flash and one swap on > > > a rotating disk? /sys/block/*/stat should be able to tell you how > > > traffic is distributed, no? > > > > That raises me a same question. Could you also look at the zswap stat > > instead of adding it into vmstat? (If zswap doesn't have the counter, > > couldn't we simply add new stat in sysfs?) > > My point is that for regular swap backends there is already > PSWP*. Distinguishing traffic between two swap backends is legitimate > of course, but zram is not really special compared to other backends > from that POV. It's only special in its memory consumption. > > zswap *is* special, though. Even though some people use it *like* a > swap backend, it's also a cache on top of swap. zswap loads and stores > do not show up in PSWP*. And they shouldn't, because in a cache > configuration, you still need the separate PSWP* stats to understand > cache eviction behavior and cache miss ratio. memory -> zswap is > ZSWPOUT; zswap -> disk is PSWPOUT; PSWPIN is a cache miss etc. > > > I thought the patch aims for exposting statistics to grab easier > > using popular meminfo and vmstat and wanted to leverage it for > > zram, too. > > Right. zram and zswap overlap in their functionality and have similar > deficits in their stats. Both should be fixed, I'm not opposing > that. But IMO we should be careful about conflating > them. Fundamentally, one is a block device, the other is an MM-native > cache layer that sits on top of block devices. Drawing false > equivalencies between them will come back to haunt us. Make sense to me.
