Re: [PATCH 04/17] mm: gup: make get_user_pages_fast and __get_user_pages_fast latency conscious

On Fri, Oct 3, 2014 at 10:07 AM, Andrea Arcangeli [off-list ref] wrote:

This teaches gup_fast and __gup_fast to re-enable irqs and
cond_resched() if possible every BATCH_PAGES.

This is disgusting.

Many (most?) __gup_fast() users just want a single page, and the
stupid overhead of the multi-page version is already unnecessary.
This just makes things much worse.

Quite frankly, we should make a single-page version of __gup_fast(),
and convert existign users to use that. After that, the few multi-page
users could have this extra latency control stuff.

And yes, the single-page version of get_user_pages_fast() is actually
latency-critical. shared futexes hit it hard, and yes, I've seen this
in profiles.

                  Linus

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>