> From: Dan Magenheimer > Subject: RE: zram /proc/swaps accounting weirdness > > > > Can you explain how this could happen if num_writes never > > > exceeded 1863? This may be harmless in the case where > > > > Odd. > > I tried to reproduce it with zram and real swap device without > > zcache but failed. Does the problem happen only if enabling zcache > > together? > > I also cannot reproduce it with only zram, without zcache. > I can only reproduce with zcache+zram. Since zcache will > only "fall through" to zram when the frontswap_store() call > in swap_writepage() fails, I wonder if in both cases swap_writepage() > is being called in large (e.g. SWAPFILE_CLUSTER-sized) blocks > of pages? When zram-only, the entire block of pages always gets > sent to zram, but with zcache only a small randomly-positioned > fraction fail frontswap_store(), but the SWAPFILE_CLUSTER-sized > blocks have already been pre-reserved on the swap device and > become only partially-filled? Urk. Never mind. My bad. When a swap page is compressed in zcache, it gets accounted in the swap subsystem as an "inuse" page for the backing swap device. (Frontswap provides a page-by-page "fronting store" for the swap device.) That explains why Used is so high for the "zram swap device" even though zram has only compressed a fraction of the pages... the remaining (much larger) number of pages have been compressed by/in zcache. Move along, there are no droids here. :-( Dan -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href