On Fri, Mar 25, 2016 at 05:00:50PM -0700, Hugh Dickins wrote: > 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. I think I found it. I have refcounting screwed up in faultaround. This should fix the problem: diff --git a/mm/filemap.c b/mm/filemap.c index 94c097ec08e7..1325bb4568d1 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2292,19 +2292,18 @@ repeat: if (fe->pte) fe->pte += iter.index - last_pgoff; last_pgoff = iter.index; - alloc_set_pte(fe, NULL, page); + if (alloc_set_pte(fe, NULL, page)) + goto unlock; unlock_page(page); - /* Huge page is mapped? No need to proceed. */ - if (pmd_trans_huge(*fe->pmd)) - break; - /* Failed to setup page table? */ - VM_BUG_ON(!fe->pte); goto next; unlock: unlock_page(page); skip: page_cache_release(page); next: + /* Huge page is mapped? No need to proceed. */ + if (pmd_trans_huge(*fe->pmd)) + break; if (iter.index == end_pgoff) break; } -- Kirill A. Shutemov -- 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
