Re: [PATCH v2] slab,slub: ignore __GFP_WAIT if we're booting orsuspending

From: Linus Torvalds
Date: Fri Jun 12 2009 - 11:05:42 EST

On Fri, 12 Jun 2009, Pekka J Enberg wrote:
> + if (system_state != SYSTEM_RUNNING)
> + local_flags &= ~__GFP_WAIT;
> +
> + might_sleep_if(local_flags & __GFP_WAIT);

This is pointless.

You're doing the "might_sleep_if()" way too late. At that point, you've
already lost 99% of all coverage, since now none of the cases of just
finding a free slab entry on the list will ever trigger that
"might_sleep()" case.

So you need to do this _early_, at the entry-point, not late, at cache
re-fill time.

So rather than removing the might_sleep_if() at the early point, and then
moving it to this late stage (because you only do the local_flags fixups
late), you need to move the local-flags fixup early instead, and do the
might_sleep_it() there.

The whole point of "might_sleep()" is that it triggers every time if
something is called in the wrong context - not just for the cases where it
actually _does_ sleep.

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