Messages in this thread | | | Date | Sat, 16 Dec 2017 18:12:35 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v19 3/7] xbitmap: add more operations |
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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.
Best, Wei
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