Messages in this thread |  | | Date | Fri, 5 Dec 2025 21:49:40 +0000 | | From | David Laight <> | | Subject | Re: [PATCH] mm: avoid use of BIT() macro for initialising VMA flags |
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On Fri, 5 Dec 2025 19:18:56 +0000 Lorenzo Stoakes <lorenzo.stoakes@oracle.com> wrote:
> On Fri, Dec 05, 2025 at 06:43:42PM +0000, David Laight wrote: > > On Fri, 5 Dec 2025 17:50:37 +0000 > > Lorenzo Stoakes <lorenzo.stoakes@oracle.com> wrote: > > > > > Commit 2b6a3f061f11 ("mm: declare VMA flags by bit") significantly changed > > > how VMA flags are declared, utilising an enum of VMA bit values and > > > ifdef-fery VM_xxx flag declarations via macro. > > > > > > As part of this change, it uses INIT_VM_FLAG() to define VM_xxx flags from > > > the newly introduced VMA bit numbers. > > > > > > However, use of this macro results in apparently unfortunate macro > > > expansion and resulted in a performance degradation.This appears to be due > > > to the (__force int), which is required for the sparse typechecking to > > > work. > > > > Does sparse complain if you just add 0? As in: > > #define INIT_VM_FLAG(name) BIT(VMA_ ## name ## _BIT + 0u) > > > > That should change the type without affecting what BIT() expands to. > > Thanks, checked that and unfortunately that doesn't satisfy sparse :)
Oh - it is that __bitwise that causes grief.
> I don't think it's too crazy to use 1UL << here, just very frustrating (TM) > that this is an issue.
Did you try getting DECLARE_VMA_BIT to define both the bit number and the bit flag and put them both into the anonymous enum? Or are there other reasons for not doing that?
> > <insert rant about C macros here>
Add rant about the compiler thinking anon enums are doing anything other than defining constants.
David
> > Cheers, Lorenzo
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