On 04/10/2019 15.10, Matthew Wilcox wrote:
On Fri, Oct 04, 2019 at 01:11:06PM +0300, Konstantin Khlebnikov wrote:
This is very slow operation. There is no reason to do it again if somebody
else already drained all per-cpu vectors after we waited for lock.
+ seq = raw_read_seqcount_latch(&seqcount);
+
mutex_lock(&lock);
+
+ /* Piggyback on drain done by somebody else. */
+ if (__read_seqcount_retry(&seqcount, seq))
+ goto done;
+
+ raw_write_seqcount_latch(&seqcount);
+
Do we really need the seqcount to do this? Wouldn't a mutex_trylock()
have the same effect?
No, this is completely different semantics.
Operation could be safely skipped only if somebody else started and
finished drain after current task called this function.
