Messages in this thread | | | Subject | Re: [RFC][PATCH] PM: Force GFP_NOIO during suspend/resume (was: Re: [linux-pm] Memory allocations in .suspend became very unreliable) | From | Benjamin Herrenschmidt <> | Date | Tue, 19 Jan 2010 08:55:57 +1100 |
| |
On Mon, 2010-01-18 at 00:00 +0100, Rafael J. Wysocki wrote: > On Sunday 17 January 2010, Benjamin Herrenschmidt wrote: > > On Sun, 2010-01-17 at 14:27 +0100, Rafael J. Wysocki wrote: > ... > > However, it's hard to deal with the case of allocations that have > > already started waiting for IOs. It might be possible to have some VM > > hook to make them wakeup, re-evaluate the situation and get out of that > > code path but in any case it would be tricky. > > In the second version of the patch I used an rwsem that made us wait for these > allocations to complete before we changed gfp_allowed_mask. > > [This is kinda buggy in the version I sent, but I'm going to send an update > in a minute.]
And nobody screamed due to cache line ping pong caused by this in the fast path ? :-)
We might want to look at something a bit smarter for that sort of read-mostly-really-really-mostly construct, though in this case I don't think RCU is the answer since we are happily scheduling.
I wonder if something per-cpu would do, it's thus the responsibility of the "writer" to take them all in order for all CPUs.
Cheers, Ben.
| |