Re: [PATCH 1/1] iomap: avoid compaction for costly folio order allocation

[IBM]

Matthew Wilcox <willy@xxxxxxxxxxxxx> writes:

> On Mon, Apr 20, 2026 at 04:33:28PM +0000, Salvatore Dipietro wrote:
>> I have submitted a v2 of the patch based on Ritesh's suggestion.
>> https://lore.kernel.org/linux-mm/20260420161404.642-1-dipiets@xxxxxxxxx/T/#u
>
> ... but without linking back to this thread, so nobody who was exposed
> to that thread for the first time knows about this one.  That's poor form.

Yup.
Also, given the Maintainers (willy, Christoph, Dave) shown their
dis-interest in taking the patch in it's current form, the right way is
to get back with performance data with both the approaches (which we
were discussing) and first get the consensus from everyone, before
proposing this as a patch :).

Having said that, we do care if a genuine performance issue gets
reported. In that context, I wanted to understand your setup a bit from
memory fragmentation perspective. Are you trying to simulate memory
fragmentation and then benchmarking? Or was this problem hitting when
you run simply run the reproduction steps mentioned in your cover
letter?


BTW - I was following the other thread too where PREEMPT_LAZY problem
was getting discussed. And from what I understood, you mentioned [1]
enabling THP on the system made that problem go away. Also it looks like
enabling THP is the right thing to do for this kind of workload. Does
that also mean enabling THP fixed this problem too? Do you still hit
memory fragmentation and/or similar throughput drop w/o this fix after
you enable THP? It will be good to know those details too please.

[1]: https://lore.kernel.org/all/20260403191942.21410-1-dipiets@xxxxxxxxx/T/#md88ca4258766e897e432df85874d197db476c7d1

-ritesh