Re: [PATCH] mm: move more expensive part of XA setup out of mapping check

[Jens Axboe]

On 10/26/21 12:08 PM, Matthew Wilcox wrote:
> On Tue, Oct 26, 2021 at 10:01:20AM -0600, Jens Axboe wrote:
>> The fast path here is not needing any writeback, yet we spend time setting
>> up the xarray lookup data upfront. Move the part that actually needs to
>> iterate the address space mapping into a separate helper, saving ~30% of
>> the time here.
> 
> No objection to this patch, but it did remind me that I never saw an answer to
> https://lore.kernel.org/all/CAHk-=wg_-EwefQ_3Osz4iJxTrTk3tfrV53Z7-jaGg=tm9i5TXg@xxxxxxxxxxxxxx/
> (and nor did lore)

Totally missed that, and yes there could be cases where that lookup is
going to be way too slow. I'll take a look.

-- 
Jens Axboe