On 2024/11/8 23:30, David Hildenbrand wrote:
On 08.11.24 05:12, Baolin Wang wrote:
Traditionally, tmpfs only supported PMD-sized huge folios. However
nowadays
with other file systems supporting any sized large folios, and extending
anonymous to support mTHP, we should not restrict tmpfs to allocating
only
PMD-sized huge folios, making it more special. Instead, we should allow
tmpfs can allocate any sized large folios.
Considering that tmpfs already has the 'huge=' option to control the huge
folios allocation, we can extend the 'huge=' option to allow any sized
huge
folios. The semantics of the 'huge=' mount option are:
huge=never: no any sized huge folios
huge=always: any sized huge folios
huge=within_size: like 'always' but respect the i_size
huge=advise: like 'always' if requested with fadvise()/madvise()
Note: for tmpfs mmap() faults, due to the lack of a write size hint,
still
allocate the PMD-sized huge folios if huge=always/within_size/advise
is set.
So, no fallback to smaller sizes for now in case we fail to allocate a
PMD one? Of course, this can be added later fairly easily.
Right. I have no strong preference on this. If no one objects, I can add
a fallback to smaller large folios if the PMD sized allocation fails in
the next version.
Moreover, the 'deny' and 'force' testing options controlled by
'/sys/kernel/mm/transparent_hugepage/shmem_enabled', still retain the
same
semantics. The 'deny' can disable any sized large folios for tmpfs, while
the 'force' can enable PMD sized large folios for tmpfs.
Any comments and suggestions are appreciated. Thanks.
Hi David,
I did not add a new Kconfig option to control the default behavior of
'huge='
in the current version. I have not changed the default behavior at this
time, and let's see if there is a need for this.
Likely we want to change the default at some point so people might get a
benefit in more scenarios automatically. But I did not investigate how
/tmp is mapped as default by Fedora, for example.
Personally, adding a cmdline to change the default value might be more
useful than the Kconfig. Anyway, I still want to investigate if there is
a real need.
