On 08.05.24 06:45, Baolin Wang wrote:
On 2024/5/7 18:52, Ryan Roberts wrote:
On 06/05/2024 09:46, Baolin Wang wrote:
To support the use of mTHP with anonymous shmem, add a new sysfs interface
'shmem_enabled' in the '/sys/kernel/mm/transparent_hugepage/hugepages-kB/'
directory for each mTHP to control whether shmem is enabled for that mTHP,
with a value similar to the top level 'shmem_enabled', which can be set to:
"always", "inherit (to inherit the top level setting)", "within_size", "advise",
"never", "deny", "force". These values follow the same semantics as the top
level, except the 'deny' is equivalent to 'never', and 'force' is equivalent
to 'always' to keep compatibility.
We decided at [1] to not allow 'force' for non-PMD-sizes.
[1]
https://lore.kernel.org/linux-mm/533f37e9-81bf-4fa2-9b72-12cdcb1edb3f@xxxxxxxxxx/
However, thinking about this a bit more, I wonder if the decision we made to
allow all hugepages-xxkB/enabled controls to take "inherit" was the wrong one.
Perhaps we should have only allowed the PMD-sized enable=inherit (this is just
for legacy back compat after all, I don't think there is any use case where
changing multiple mTHP size controls atomically is actually useful). Applying
Agree. This is also our usage of 'inherit'.
that pattern here, it means the top level can always take "force" without any
weird error checking. And we would allow "force" on the PMD-sized control but
not on the others - again this is easy to error check.
Does this pattern make more sense? If so, is it too late to change
hugepages-xxkB/enabled interface?
IMO, this sounds reasonable to me. Let's see what others think, David?
Likely too late and we should try not to diverge too much from "enabled"
for "shmem_enabled".
Having that said, to me it's much cleaner to just have "inherit" for all
sizes and disallow invalid configurations as discussed.
Error checking cannot be too hard unless I am missing something important :)
--
Cheers,
David / dhildenb
