On Fri, 25 Mar 2016, Kirill A. Shutemov wrote: > On Thu, Mar 24, 2016 at 12:08:55PM -0700, Hugh Dickins wrote: > > On Thu, 24 Mar 2016, Kirill A. Shutemov wrote: > > > On Wed, Mar 23, 2016 at 01:09:05PM -0700, Hugh Dickins wrote: > > > > The small files thing formed my first impression. My second > > > > impression was similar, when I tried mmap(NULL, size_of_RAM, > > > > PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_SHARED, -1, 0) and > > > > cycled around the arena touching all the pages (which of > > > > course has to push a little into swap): that soon OOMed. > > > > > > > > But there I think you probably just have some minor bug to be fixed: > > > > I spent a little while trying to debug it, but then decided I'd > > > > better get back to writing to you. I didn't really understand what > > > > I was seeing, but when I hacked some stats into shrink_page_list(), > > > > converting !is_page_cache_freeable(page) to page_cache_references(page) > > > > to return the difference instead of the bool, a large proportion of > > > > huge tmpfs pages seemed to have count 1 too high to be freeable at > > > > that point (and one huge tmpfs page had a count of 3477). > > > > > > I'll reply to your other points later, but first I wanted to address this > > > obvious bug. > > > > Thanks. That works better, but is not yet right: memory isn't freed > > as it should be, so when I exit then try to run a second time, the > > mmap() just gets ENOMEM (with /proc/sys/vm/overcommit_memory 0): > > MemFree is low. No rush to fix, I've other stuff to do. > > > > I don't get as far as that on the laptop, since the first run is OOM > > killed while swapping; but I can't vouch for the OOM-kill-correctness > > of the base tree I'm using, and this laptop has a history of OOMing > > rather too easily if all's not right. > > Hm. I don't see the issue. > > I tried to reproduce it in my VM with following script: > > #!/bin/sh -efu > > swapon -a > > ram="$(grep MemTotal /proc/meminfo | sed 's,[^0-9\]\+,,; s, kB,k,')" > > usemem -w -f /dev/zero "$ram" > > swapoff -a > swapon -a > > usemem -w -f /dev/zero "$ram" > > cat /proc/meminfo > grep thp /proc/vmstat > > ----- > > usemem is a tool from this archive: > > http://www.spinics.net/lists/linux-mm/attachments/gtarazbJaHPaAT.gtar > > It works fine even if would double size of mapping. > > Do you have a reproducer? Yes, my reproducer is simpler (just cycling twice around the arena, touching each page in order); and I too did not see it running your script using usemem above. It looks as if that invocation isn't doing enough work with swap: if I add a "-r 2" to those usemem lines, then I get "usemem: mmap failed: Cannot allocate memory" on the second. I also added a "sleep 2" before the second call to usemem: I'm not sure of the current state of vmstat, but historically it's slow to gather back from each cpu to global, and I think it used to leave some cpu counts stranded indefinitely once upon a time. In my own testing, I have a /proc/sys/vm/stat_refresh to touch before checking meminfo or vmstat - and I think the vm_enough_memory() check in mmap() may need that same care, since it refers to NR_FREE_PAGES etc. 8GB is my ramsize, if that matters. Hugh -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
