Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag | Date | Tue, 11 Aug 2020 17:22:54 +0200 |
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Thomas Gleixner <tglx@linutronix.de> writes: > Michal Hocko <mhocko@suse.com> writes: >> zone->lock should be held for a very limited amount of time. > > Emphasis on should. free_pcppages_bulk() can hold it for quite some time > when a large amount of pages are purged. We surely would have converted > it to a raw lock long time ago otherwise. > > For regular enterprise stuff a few hundred microseconds might qualify as > a limited amount of time. For advanced RT applications that's way beyond > tolerable..
Sebastian just tried with zone lock converted to a raw lock and maximum latencies go up by a factor of 7 when putting a bit of stress on the memory subsytem. Just a regular kernel compile kicks them up by a factor of 5. Way out of tolerance.
We'll have a look whether it's solely free_pcppages_bulk() and if so we could get away with dropping the lock in the loop.
Thanks,
tglx
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