Messages in this thread | | | Subject | Re: [Cluster-devel] [PATCH v6 10/19] gfs2: Introduce flag for glock holder auto-demotion | From | Bob Peterson <> | Date | Mon, 23 Aug 2021 11:36:10 -0500 |
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On 8/23/21 11:05 AM, Matthew Wilcox wrote: > On Mon, Aug 23, 2021 at 05:18:12PM +0200, Andreas Gruenbacher wrote: >> On Mon, Aug 23, 2021 at 10:14 AM Steven Whitehouse <swhiteho@redhat.com> wrote: >>> If the goal here is just to allow the glock to be held for a longer >>> period of time, but with occasional interruptions to prevent >>> starvation, then we have a potential model for this. There is >>> cond_resched_lock() which does this for spin locks. >> >> This isn't an appropriate model for what I'm trying to achieve here. >> In the cond_resched case, we know at the time of the cond_resched call >> whether or not we want to schedule. If we do, we want to drop the spin >> lock, schedule, and then re-acquire the spin lock. In the case we're >> looking at here, we want to fault in user pages. There is no way of >> knowing beforehand if the glock we're currently holding will have to >> be dropped to achieve that. In fact, it will almost never have to be >> dropped. But if it does, we need to drop it straight away to allow the >> conflicting locking request to succeed. > > It occurs to me that this is similar to the wound/wait mutexes > (include/linux/ww_mutex.h & Documentation/locking/ww-mutex-design.rst). > You want to mark the glock as woundable before faulting, and then discover > if it was wounded after faulting. Maybe sharing this terminology will > aid in understanding? > Hmm. Woundable. I like it. Andreas and I argued about the terminology but we never found a middle-ground. Perhaps this is it. Thanks, Matthew.
Regards,
Bob Peterson
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