Re: kswapd0: page allocation failure: order:0, mode:0x820(GFP_ATOMIC), nodemask=(null),cpuset=/,mems_allowed=0 (Kernel v6.5.9, 32bit ppc)

Sergey Senozhatsky
2024-06-06T05:43:39Z

On (24/06/06 12:46), Chengming Zhou wrote:
> >> Agree, I think we should try to improve locking scalability of zsmalloc.
> >> I have some thoughts to share, no code or test data yet:
> >>
> >> 1. First, we can change the pool global lock to per-class lock, which
> >> is more fine-grained.
> >
> > Commit c0547d0b6a4b6 "zsmalloc: consolidate zs_pool's migrate_lock
> > and size_class's locks" [1] claimed no significant difference
> > between class->lock and pool->lock.
>
> Ok, I haven't looked into the history much, that seems preparation of trying
> to introduce reclaim in the zsmalloc? Not sure. But now with the reclaim code
> in zsmalloc has gone, should we change back to the per-class lock? Which is

Well, the point that commit made was that Nhat (and Johannes?) were
unable to detect any impact of pool->lock on a variety of cases. So
we went on with code simplification.

> obviously more fine-grained than the pool lock. Actually, I have just done it,
> will test to get some data later.

Thanks, we'll need data on this. I'm happy to take the patch, but
jumping back and forth between class->lock and pool->lock merely
"for obvious reasons" is not what I'm extremely excited about.