Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag | Date | Thu, 13 Aug 2020 18:14:32 +0200 |
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Matthew Wilcox <willy@infradead.org> writes: > On Thu, Aug 13, 2020 at 03:27:15PM +0200, Thomas Gleixner wrote: >> And guarding it with RT is not working either because then you are back >> to square one with the problem which triggered the discussion in the >> first place: >> >> raw_spin_lock() >> alloc() >> if (RT && !preemptible()) <- False because RT == false >> goto bail; >> >> spin_lock(&zone->lock) --> LOCKDEP complains >> >> So either you convince Paul not to do that or you need to do something >> like I suggested in my other reply. > > I'd like to throw in the possibility that we do something like: > > raw_spin_lock() > alloc() > if (!spin_trylock(&zone->lock)) > if (RT && !preemptible()) > goto bail; > spin_lock(&zone->lock); > > would that make us feel more comfortable about converting zone->lock to > a raw spinlock?
Even if that could cure that particular problem of allocations in deep atomic context, making zone->lock raw brings back the problem of zone->lock being held/contended for hundreds of microseconds with interrupts disabled which is causing RT tasks to miss their deadlines by big margins.
Thanks,
tglx
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