I would like to report a regression in XFS introduced in kerenel v6.6 in
commit 5d8edfb900d5 ("iomap: Copy larger chunks from userspace"). On a
system running under Xen, when a process creates a file on an XFS file
system and writes exactly 2MB or more in a single write syscall,
accessing memory through mmap on that file causes the process to hang,
while dmesg is flooded with page fault warnings:
[ 62.406493] </TASK>
As shown in the log above, the issue persists in kernel 6.6.59. However,
it was recently resolved in commit 2b0f922323cc ("mm: don't install PMD
mappings when THPs are disabled by the hw/process/vma"). The fix was
backported to 6.11. Would it make sense to backport it to 6.6 as well?
I encountered this issue while updating a Gentoo VM with an XFS
filesystem running under Xen. During a final stage of glibc update,
files were copied to the live system, but when locale-gen started, it
hung. I couldn't open a new shell, as it attempted to mmap an
LC_COLLATE-related file, resulting in the same page faults as reported
above.