Re: [PATCH v2] nvme: provide fallback for discard alloc failure

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On 12/12/18 9:28 AM, Keith Busch wrote:
> On Wed, Dec 12, 2018 at 09:18:11AM -0700, Jens Axboe wrote:
>> When boxes are run near (or to) OOM, we have a problem with the discard
>> page allocation in nvme. If we fail allocating the special page, we
>> return busy, and it'll get retried. But since ordering is honored for
>> dispatch requests, we can keep retrying this same IO and failing. Behind
>> that IO could be requests that want to free memory, but they never get
>> the chance.
>>
>> Allocate a fixed discard page per controller for a safe fallback, and use
>> that if the initial allocation fails.
> 
> Do we need to allocate this per controller? One page for the whole driver
> may be sufficient to make forward progress, right?

It should be, but that might create a shit storm if we're OOM and have
tons of drives. I think one per controller is saner, and it's dwarfed
by memory we consume anyway in static allocations.

-- 
Jens Axboe




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