On Tue, May 08, 2007 at 01:22:56PM +0100, David Howells wrote:
> Nick Piggin <[email protected]> wrote:
>
> > This patch (along with the subsequent one to optimise unlock_page) reduces
> > the overhead of lock_page/unlock_page (measured with page faults and a patch
> > to lock the page in the fault handler) by about 425 cycles on my 2-way G5.
>
> Seems reasonable, though test_and_set_lock_bit() might be a better name.
The postfix attaches lock semantics to the test_and_set_bit operation,
so I don't think it is necessarily wrong to have this name. But it doesn't
matter too much I guess.
> > +There are two special bitops with lock barrier semantics (acquire/release,
> > +same as spinlocks).
>
> You should update Documentation/memory-barriers.txt also.
Will do.
> > #define TestSetPageLocked(page) \
> > test_and_set_bit(PG_locked, &(page)->flags)
> > +#define TestSetPageLocked_Lock(page) \
> > + test_and_set_bit_lock(PG_locked, &(page)->flags)
>
> Can we get away with just moving TestSetPageLocked() to the new function
> rather than adding another accessor? Or how about LockPageLocked() and
> UnlockPageLocked() rather than SetPageLocked_Lock() that last looks wrong
> somehow.
The problem is that it implies some semantics that it may not have. Possibly
better is to just remove them all and use only trylock/lock/unlock_page.
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