Wei Wang wrote: > On 12/16/2017 02:42 AM, Matthew Wilcox wrote: > > On Tue, Dec 12, 2017 at 07:55:55PM +0800, Wei Wang wrote: > >> +int xb_preload_and_set_bit(struct xb *xb, unsigned long bit, gfp_t gfp); > > I'm struggling to understand when one would use this. The xb_ API > > requires you to handle your own locking. But specifying GFP flags > > here implies you can sleep. So ... um ... there's no locking? > > In the regular use cases, people would do xb_preload() before taking the > lock, and the xb_set/clear within the lock. > > In the virtio-balloon usage, we have a large number of bits to set with > the balloon_lock being held (we're not unlocking for each bit), so we > used the above wrapper to do preload and set within the balloon_lock, > and passed in GFP_NOWAIT to avoid sleeping. Probably we can change to > put this wrapper implementation to virtio-balloon, since it would not be > useful for the regular cases. GFP_NOWAIT is chosen in order not to try to OOM-kill something, isn't it? But passing GFP_NOWAIT means that we can handle allocation failure. There is no need to use preload approach when we can handle allocation failure.
