Re: [PATCH v5 4/6] mm: shmem: add mTHP support for anonymous shmem

[Bang Li]

Hey Ryan,

On 2024/7/4 21:58, Ryan Roberts wrote:
> > > Then for tmpfs, which doesn't support non-PMD-sizes yet, we just always use the
> > > PMD-size control for decisions.
> > >
> > > I'm also really struggling with the concept of shmem_is_huge() existing along
> > > side shmem_allowable_huge_orders(). Surely this needs to all be refactored into
> > > shmem_allowable_huge_orders()?
> > I understood. But now they serve different purposes: shmem_is_huge() will be
> > used to check the huge orders for the top level, for*tmpfs*  and anon shmem;
> > whereas shmem_allowable_huge_orders() will only be used to check the per-size
> > huge orders for anon shmem (excluding tmpfs now). However, as I plan to add mTHP
> > support for tmpfs, I think we can perform some cleanups.
> >
> > > > +    /* Allow mTHP that will be fully within i_size. */
> > > > +    order = highest_order(within_size_orders);
> > > > +    while (within_size_orders) {
> > > > +        index = round_up(index + 1, order);
> > > > +        i_size = round_up(i_size_read(inode), PAGE_SIZE);
> > > > +        if (i_size >> PAGE_SHIFT >= index) {
> > > > +            mask |= within_size_orders;
> > > > +            break;
> > > > +        }
> > > > +
> > > > +        order = next_order(&within_size_orders, order);
> > > > +    }
> > > > +
> > > > +    if (vm_flags & VM_HUGEPAGE)
> > > > +        mask |= READ_ONCE(huge_shmem_orders_madvise);
> > > > +
> > > > +    if (global_huge)
> > > Perhaps I've misunderstood global_huge, but I think its just the return value
> > > from shmem_is_huge()? But you're also using shmem_huge directly in this
> > Yes.
> >
> > > function. I find it all rather confusing.
> > I think I have explained why need these logics as above. Since mTHP support for
> > shmem has just started (tmpfs is still in progress). I will make it more clear
> > in the following patches.
> OK as long as you have a plan for the clean up, that's good enough for me.

Can I continue to push the following patch [1]? When other types of 
shmem mTHP
are supported, we will perform cleanups uniformly.

[1] 
https://lore.kernel.org/linux-mm/20240702023401.41553-1-libang.li@xxxxxxxxxxxx/

Thanks,
Bang