Re: Endless calls to xas_split_alloc() due to corrupted xarray entry

[Linus Torvalds]

On Wed, 19 Jun 2024 at 07:31, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> Actually, it's 11.  We can't split an order-12 folio because we'd have
> to allocate two levels of radix tree, and I decided that was too much
> work.  Also, I didn't know that ARM used order-13 PMD size at the time.
>
> I think this is the best fix (modulo s/12/11/).

Can we use some more descriptive thing than the magic constant 11 that
is clearly very subtle.

Is it "XA_CHUNK_SHIFT * 2 - 1"

IOW, something like

   #define MAX_XAS_ORDER (XA_CHUNK_SHIFT * 2 - 1)
   #define MAX_PAGECACHE_ORDER min(HPAGE_PMD_ORDER,12)

except for the non-TRANSPARENT_HUGEPAGE case where it currently does

  #define MAX_PAGECACHE_ORDER    8

and I assume that "8" is just "random round value, smaller than 11"?

             Linus