Messages in this thread | | | Date | Sun, 14 Mar 2021 21:37:27 -0600 | From | Yu Zhao <> | Subject | Re: [PATCH v1 10/14] mm: multigenerational lru: core |
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On Sun, Mar 14, 2021 at 07:02:01PM -0700, Andi Kleen wrote: > Yu Zhao <yuzhao@google.com> writes:
Hi Andi!
Recovering the context a bit:
err = -EBUSY;
> > + > > +#ifdef CONFIG_MEMCG > > + if (memcg && atomic_read(&memcg->moving_account)) > > + goto contended; > > +#endif > > + if (!mmap_read_trylock(mm)) > > + goto contended; > > These are essentially spinloops. Surely you need a cpu_relax() somewhere?
contended: ... cond_resched(); } while (err == -EAGAIN && !mm_is_oom_victim(mm) && !mm_has_migrated(mm, memcg));
So if it's contended, we break the loop.
> In general for all of spinloop like constructs it would be useful to > consider how to teach lockdep about them. > > > + do { > > + old_flags = READ_ONCE(page->flags); > > + new_gen = ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1; > > + VM_BUG_ON_PAGE(new_gen < 0, page); > > + if (new_gen >= 0 && new_gen != old_gen) > > + goto sort; > > + > > + new_gen = (old_gen + 1) % MAX_NR_GENS; > > + new_flags = (old_flags & ~LRU_GEN_MASK) | ((new_gen + 1UL) << LRU_GEN_PGOFF); > > + /* mark page for reclaim if pending writeback */ > > + if (front) > > + new_flags |= BIT(PG_reclaim); > > + } while (cmpxchg(&page->flags, old_flags, new_flags) != > > old_flags); > > I see this cmpxchg flags pattern a lot. Could there be some common code > factoring?
Thanks for noticing this. A shorthand macro would be nice. Hmm... let me investigate. I don't know how to do this off the top of my head:
A macro can be used like
cmpxchg_macro() { func(); }
without backslashes and it'll be expanded to
do { func(); } while ();
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