On Wed, Apr 29, 2020 at 06:40:02PM +0300, Kirill A. Shutemov wrote:
> On Wed, Apr 29, 2020 at 06:36:32AM -0700, Matthew Wilcox wrote:
> > From: "Matthew Wilcox (Oracle)" <[email protected]>
> >
> > This patch set does not pass xfstests. Test at your own risk. It is
> > based on the readahead rewrite which is in Andrew's tree. The large
> > pages somehow manage to fall off the LRU, so the test VM quickly runs
> > out of memory and freezes. To reproduce:
> >
> > # mkfs.xfs /dev/sdb && mount /dev/sdb /mnt && dd if=/dev/zero bs=1M
> > count=2048 of=/mnt/bigfile && sync && sleep 2 && sync && echo 1
> > >/proc/sys/vm/drop_caches
> > # /host/home/willy/kernel/xarray-2/tools/vm/page-types | grep thp
> > 0x0000000000401800 511 1
> > ___________Ma_________t____________________ mmap,anonymous,thp
> > 0x0000000000405868 1 0
> > ___U_lA____Ma_b_______t____________________
> > uptodate,lru,active,mmap,anonymous,swapbacked,thp
> > # dd if=/mnt/bigfile of=/dev/null bs=2M count=5
> > # /host/home/willy/kernel/xarray-2/tools/vm/page-types | grep thp
> > 0x0000000000400000 2516 9
> > ______________________t____________________ thp
> > 0x0000000000400028 1 0
> > ___U_l________________t____________________ uptodate,lru,thp
> > 0x000000000040006c 106 0
> > __RU_lA_______________t____________________
> > referenced,uptodate,lru,active,thp
>
> Note that you have 107 pages on LRU. It is only head pages. With order-5
> pages it is over 13MiB.
>
> Looks like everything is fine.
/proc/kpageflags reads page's flag bit directly instead of relying on
PageLRU:
u |= kpf_copy_bit(k, KPF_LRU, PG_lru);
Tail pages don't have this bit set. They rely on head page's flag for
PageLRU().
It would be nice to get it fixed, but I guess it is too late. Somebody may
rely on the current behaviour by now.
--
Kirill A. Shutemov
