Messages in this thread | | | From | David Howells <> | Subject | Re: [PATCH 11/11] afs: Fix dirty-region encoding on ppc32 with 64K pages | Date | Wed, 28 Oct 2020 17:27:52 +0000 |
| |
Matthew Wilcox <willy@infradead.org> wrote:
> > > > +{ > > > > + if (PAGE_SIZE - 1 <= __AFS_PAGE_PRIV_MASK) > > > > + return 1; > > > > + else > > > > + return PAGE_SIZE / (__AFS_PAGE_PRIV_MASK + 1); > > > > > > Could this be DIV_ROUND_UP(PAGE_SIZE, __AFS_PAGE_PRIV_MASK + 1); avoiding > > > a conditional? I appreciate it's calculated at compile time today, but > > > it'll be dynamic with THP. > > > > Hmmm - actually, I want a shift size, not a number of bytes as I divide by it > > twice in afs_page_dirty(). > > __AFS_PAGE_PRIV_MASK is a constant though. If your compiler can't > optimise a divide-by-a-constant-power-of-two into a shift-by-a-constant (*), > it's time to get yourself a new compiler. > > (*) assuming that's faster on the CPU it's targetting.
I'm dividing by the resolution, which is calculated from the page size - which in a THP world is variable:
static inline unsigned long afs_page_dirty(size_t from, size_t to) { size_t res = afs_page_dirty_resolution(); from /= res; /* Round down */ to = (to - 1) / res; /* Round up */ return ((unsigned long)to << __AFS_PAGE_PRIV_SHIFT) | from; }
David
| |