On Sun, Dec 17, 2017 at 01:47:21PM +0000, Wang, Wei W wrote: > On Saturday, December 16, 2017 3:22 AM, Matthew Wilcox wrote: > > On Fri, Dec 15, 2017 at 10:49:15AM -0800, Matthew Wilcox wrote: > > > Here's the API I'm looking at right now. The user need take no lock; > > > the locking (spinlock) is handled internally to the implementation. > > Another place I saw your comment " The xb_ API requires you to handle your own locking" which seems conflict with the above "the user need take no lock". > Doesn't the caller need a lock to avoid concurrent accesses to the ida bitmap? Yes, the xb_ implementation requires you to handle your own locking. The xbit_ API that I'm proposing will take care of the locking for you. There's also no preallocation in the API. > We'll change it to "bool xb_find_set(.., unsigned long *result)", returning false indicates no "1" bit is found. I put a replacement proposal in the next paragraph: bool xbit_find_set(struct xbitmap *, unsigned long *start, unsigned long max); Maybe 'start' is the wrong name for that parameter. Let's call it 'bit'. It's both "where to start" and "first bit found". > > - xbit_clear() can't return an error. Neither can xbit_zero(). > > I found the current xbit_clear implementation only returns 0, and there isn't an error to be returned from this function. In this case, is it better to make the function "void"? Yes, I think so. My only qualm is that I've been considering optimising the memory consumption when an entire 1024-bit chunk is full; instead of keeping a pointer to a 128-byte entry full of ones, store a special value in the radix tree which means "every bit is set". The downside is that we then have to pass GFP flags to xbit_clear() and xbit_zero(), and they can fail. It's not clear to me whether that's a good tradeoff. > Are you suggesting to rename the current xb_ APIs to the above xbit_ names (with parameter changes)? > > Why would we need xbit_alloc, which looks like ida_get_new, I think set/clear should be adequate to the current usages. I'm intending on replacing the xb_ and ida_ implementations with this one. It removes the preload API which makes it easier to use, and it handles the locking for you. But I need to get the XArray (which replaces the radix tree) finished first.
