On Tue, 2022-02-08 at 12:47 -0300, Marcelo Tosatti wrote: > > Changes since RFC: > > - Avoid unnecessary spin_lock_irqsave/restore() in free_pcppages_bulk() > > - Add more detail to commit and code comments. > > - Use synchronize_rcu() instead of synchronize_rcu_expedited(), the RCU > > documentation says to avoid it unless really justified. I don't think > > it's justified here, if we can schedule and join works, waiting for > > an RCU grace period is OK. > > https://patchwork.ozlabs.org/project/netdev/patch/1306228052.3026.16.camel@edumazet-laptop/ > > Adding 100ms to direct reclaim path might be problematic. It will also > slowdown kcompactd (note it'll call drain_all_pages for each zone). I did some measurements on an idle machine, worst case was ~30ms. I agree that might too much for direct reclaim, so I'll switch back to expedited and add a comment. > > - Avoid sparse warnings by using rcu_access_pointer() and > > rcu_dereference_protected(). > > > > include/linux/mmzone.h | 22 +++++- > > mm/page_alloc.c | 155 ++++++++++++++++++++++++++--------------- > > mm/vmstat.c | 6 +- > > 3 files changed, 120 insertions(+), 63 deletions(-) > > > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > > index b4cb85d9c6e8..b0b593fd8e48 100644 > > --- a/include/linux/mmzone.h > > +++ b/include/linux/mmzone.h > > @@ -388,13 +388,31 @@ struct per_cpu_pages { > > short expire; /* When 0, remote pagesets are drained */ > > #endif > > > > - struct pcplists *lp; > > + /* > > + * As a rule of thumb, any access to struct per_cpu_pages's 'lp' has > > + * happen with the pagesets local_lock held and using > > + * rcu_dereference_check(). If there is a need to modify both > > + * 'lp->count' and 'lp->lists' in the same critical section 'pcp->lp' > > + * can only be derefrenced once. See for example: > > Typo. Noted. Thanks! -- Nicolás Sáenz
