Re: [PATCH v3 2/4] mm: kick writeback flusher for IOCB_DONTCACHE with targeted dirty tracking

Jeff Layton
2026-04-27T10:51:16Z

On Sun, 2026-04-26 at 21:44 +0100, Matthew Wilcox wrote:
> On Sun, Apr 26, 2026 at 07:56:08AM -0400, Jeff Layton wrote:
> > Mixed-mode noisy neighbor (dontcache writer + buffered readers):
> > baseline patched change
> > writer (MB/s) 1297.6 1471.1 +13.4%
> > readers avg (MB/s) 855.0 462.4 -45.9%
>
> hm. This wasn't what I thought of when I thought of "noisy neighbour".
> I'd have process A doing DONTCACHE writes to file A and process B doing
> normal buffered writes to file B.

Originally, I was benchmarking this via nfsd and only later did I add
the suite for local benchmarks. With nfsd, setting the iomode affects
all reads or writes.

So initially, I had it testing them with both reads and writes set to
the same setting, but then later I decided to play with different modes
for reads and writes. The best performing one was buffered reads +
dontcache writes. It's possible a mix of different modes will be better
on a local fs.

I can't easily do a benchmark like you're suggesting with nfsd, but it
should be possible on a local benchmark. I'll see what I can come up
with.

Thanks,
--
Jeff Layton <jlayton@kernel.org>