Messages in this thread | | | Date | Wed, 28 Oct 2020 17:11:59 +0000 | From | Matthew Wilcox <> | Subject | Re: [PATCH 11/11] afs: Fix dirty-region encoding on ppc32 with 64K pages |
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On Wed, Oct 28, 2020 at 05:05:08PM +0000, David Howells wrote: > 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.
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