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.
