On Sat, 2024-10-12 at 13:05 -0700, Yang Shi wrote:
> On Sat, Oct 12, 2024 at 8:38 AM Avi Kivity <avi@xxxxxxxxxxxx> wrote:
> >
> > On Fri, 2024-10-11 at 15:29 -0700, Yang Shi wrote:
> > > On Wed, Oct 9, 2024 at 9:04 AM Avi Kivity <avi@xxxxxxxxxxxx>
> > > wrote:
> > > >
> > > > On Linux 6.10.10 with CONFIG_READ_ONLY_THP_FOR_FS=y,
> > > > madvise(MADV_COLLAPSE) on program text fails with EINVAL.
> > > >
> > > > To reproduce, compile the reproducer with
> > > >
> > > > clang -g -o text-hugepage text-hugepage.c \
> > > > -fuse-ld=lld \
> > > > -Wl,-zcommon-page-size=2097152 -Wl,-zmax-page-
> > > > size=2097152
> > > > \
> > > > -Wl,-z,separate-loadable-segments
> > > >
> > > > and run:
> > >
> > > Didn't clang make the page cache dirty?
> > >
> > > Having sync between clang and the execution made the problem go
> > > away
> > > for me.
> > >
> >
> > I see it even with sync (and msync just before the madvise calls).
>
> Did you stop khugepaged? It may race with MADV_COLLAPSE. If it failed
> due to race with khugepaged, you should see -EAGAIN instead of
> -EINVAL.
I did not, but I don't imagine I hit the race in all my attempts.
>
> I did the below commands in a loop for 1000 times, it never failed (I
> modified the test program a little bit to print out failure if
> MADV_COLLAPSE returns failure). I had khugepaged stopped and ran the
> test on v6.12-rc1 kernel on my AmpereOne machine.
>
> rm text-hugepage
> clang -g -o text-hugepage text-hugepage.c -fuse-ld=lld
> -Wl,-zcommon-page-size=2097152 -Wl,-zmax-page-size=2097152
> -Wl,-z,separate-loadable-segments
> sync
> ./text-hugepage
>
> >
> >
> > Tracing shows this (last lines before syscall exit):
> >
> > > hpage_collapse_scan_file() {
> > > __rcu_read_lock();
> > > __rcu_read_unlock();
> > > }
>
> It meant collapse_file() was not called at all.
> hpage_collapse_scan_file() failed. A couple of reasons may fail it,
> for example, refcount is not expected, not on lru, etc. You can trace
> huge_memory:mm_khugepaged_scan_file to get more information about the
> failure.
text-hugepage-689146 [023] 200457.073794: mm_khugepaged_scan_file:
mm=0xffff92fc512aac00, scan_pfn=0x5a4310, filename=text-hugepage,
present=0, swap=0, result=page_compound
