On Thu, Oct 17, 2024 at 05:34:15PM +0800, Baolin Wang wrote: > + Kirill > > On 2024/10/16 22:06, Matthew Wilcox wrote: > > On Thu, Oct 10, 2024 at 05:58:10PM +0800, Baolin Wang wrote: > > > Considering that tmpfs already has the 'huge=' option to control the THP > > > allocation, it is necessary to maintain compatibility with the 'huge=' > > > option, as well as considering the 'deny' and 'force' option controlled > > > by '/sys/kernel/mm/transparent_hugepage/shmem_enabled'. > > > > No, it's not. No other filesystem honours these settings. tmpfs would > > not have had these settings if it were written today. It should simply > > ignore them, the way that NFS ignores the "intr" mount option now that > > we have a better solution to the original problem. > > > > To reiterate my position: > > > > - When using tmpfs as a filesystem, it should behave like other > > filesystems. > > - When using tmpfs to implement MAP_ANONYMOUS | MAP_SHARED, it should > > behave like anonymous memory. > > I do agree with your point to some extent, but the ‘huge=’ option has > existed for nearly 8 years, and the huge orders based on write size may not > achieve the performance of PMD-sized THP in some scenarios, such as when the > write length is consistently 4K. So, I am still concerned that ignoring the > 'huge' option could lead to compatibility issues. Yeah, I don't think we are there yet to ignore the mount option. Maybe we need to get a new generic interface to request the semantics tmpfs has with huge= on per-inode level on any fs. Like a set of FADV_* handles to make kernel allocate PMD-size folio on any allocation or on allocations within i_size. I think this behaviour is useful beyond tmpfs. Then huge= implementation for tmpfs can be re-defined to set these per-inode FADV_ flags by default. This way we can keep tmpfs compatible with current deployments and less special comparing to rest of filesystems on kernel side. If huge= is not set, tmpfs would behave the same way as the rest of filesystems. -- Kiryl Shutsemau / Kirill A. Shutemov
