On 13.06.24 10:13, Luis Chamberlain wrote:
On Thu, Jun 13, 2024 at 10:07:15AM +0200, David Hildenbrand wrote:
On 13.06.24 09:57, Luis Chamberlain wrote:
On Wed, Jun 12, 2024 at 08:08:15PM +0100, Matthew Wilcox wrote:
On Fri, Jun 07, 2024 at 02:58:57PM +0000, Pankaj Raghav (Samsung) wrote:
From: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
Usually the page cache does not extend beyond the size of the inode,
therefore, no PTEs are created for folios that extend beyond the size.
But with LBS support, we might extend page cache beyond the size of the
inode as we need to guarantee folios of minimum order. Cap the PTE range
to be created for the page cache up to the max allowed zero-fill file
end, which is aligned to the PAGE_SIZE.
I think this is slightly misleading because we might well zero-fill
to the end of the folio. The issue is that we're supposed to SIGBUS
if userspace accesses pages which lie entirely beyond the end of this
file. Can you rephrase this?
(from mmap(2))
SIGBUS Attempted access to a page of the buffer that lies beyond the end
of the mapped file. For an explanation of the treatment of the
bytes in the page that corresponds to the end of a mapped file
that is not a multiple of the page size, see NOTES.
The code is good though.
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Since I've been curating the respective fstests test to test for this
POSIX corner case [0] I wanted to enable the test for tmpfs instead of
skipping it as I originally had it, and that meant also realizing mmap(2)
specifically says this now:
Huge page (Huge TLB) mappings
Confusion alert: this likely talks about hugetlb (MAP_HUGETLB), not THP and
friends.
So it might not be required for below changes.
Thanks, I had to ask as we're dusting off this little obscure corner of
the universe. Reason I ask, is the test fails for tmpfs with huge pages,
and this patch fixes it, but it got me wondering the above applies also
to tmpfs with huge pages.
Is it tmpfs with THP/large folios or shmem with hugetlb? I assume the
tmpfs with THP. There are not really mmap/munmap restrictions to THP and
friends (because it's supposed to be "transparent" :) ).
--
Cheers,
David / dhildenb
