On Tue, Sep 27, 2022 at 10:06:23PM +0000, Sean Christopherson wrote:
> On Mon, Sep 26, 2022, Ricardo Koller wrote:
> > On Thu, Sep 22, 2022 at 07:32:42PM +0000, Sean Christopherson wrote:
> > > On Thu, Sep 22, 2022, Ricardo Koller wrote:
> > > > + void *hva = (void *)region->region.userspace_addr;
> > > > + uint64_t paging_size = region->region.memory_size;
> > > > + int ret, fd = region->fd;
> > > > +
> > > > + if (fd != -1) {
> > > > + ret = fallocate(fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> > > > + 0, paging_size);
> > > > + TEST_ASSERT(ret == 0, "fallocate failed, errno: %d\n", errno);
> > > > + } else {
> > > > + if (is_backing_src_hugetlb(region->backing_src_type))
> > > > + return false;
> > >
> > > Why is hugetlb disallowed? I thought anon hugetlb supports MADV_DONTNEED?
> > >
> >
> > It fails with EINVAL (only tried on arm) for both the PAGE_SIZE and the huge
> > page size. And note that the address is aligned as well.
> >
> > madvise(0xffffb7c00000, 2097152, MADV_DONTNEED) = -1 EINVAL (Invalid argument)
> > ^^^^^^^^^^^^^^ ^^^^^^^
> > 2M aligned 2M (hugepage size)
> >
> > madvise(0xffff9e800000, 4096, MADV_DONTNEED) = -1 EINVAL (Invalid argument)
> > ^^^^
> > PAGE_SIZE
>
> I think this needs to be root caused before merging. Unless I'm getting turned
> around, MADV_DONTEED should work, i.e. there is a test bug lurking somewhere.
Turns out that the failure is documented. Found this in the madvise manpage:
MADV_DONTNEED cannot be applied to locked pages, Huge TLB pages, or VM_PFNMAP pages.
Was also playing with the following non-selftest program (before checking the
manpage, and I now remember that I actually read the above sentence before).
This fails on both x86 and arm:
#include <stdio.h>
#include <stddef.h>
#include <sys/mman.h>
#include <linux/mman.h>
#include <assert.h>
#define SZ_2M (1 << 21)
int main()
{
void *p = mmap(NULL, SZ_2M, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB | MAP_HUGE_2MB,
-1, 0);
assert(p != MAP_FAILED);
assert(madvise(p, 4096, MADV_DONTNEED) == 0); // this fails
assert(madvise(p, SZ_2M, MADV_DONTNEED) == 0); // this fails
}
And for completeness, this passes on both:
int main()
{
void *p = mmap(NULL, SZ_2M, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
assert(p != MAP_FAILED);
assert(madvise(p, SZ_2M, MADV_DONTNEED) == 0);
}
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