linux-kernel - RE: [RFC] Order 4 allocation failures in the MEI client driver

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Message-ID: <PH7PR11MB7605E466FDE32774B0F2E426E58C2@PH7PR11MB7605.namprd11.prod.outlook.com>
Date: Mon, 19 Aug 2024 16:46:52 +0000
From: "Winkler, Tomas" <tomas.winkler@...el.com>
To: Arnd Bergmann <arnd@...db.de>, Rohit Agarwal <rohiagar@...omium.org>, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Usyskin,
 Alexander" <alexander.usyskin@...el.com>, "Lubart, Vitaly"
	<vitaly.lubart@...el.com>
Subject: RE: [RFC] Order 4 allocation failures in the MEI client driver

> On Tue, Aug 13, 2024, at 10:45, Rohit Agarwal wrote:
> > Hi All,
> >
> > I am seeing an inconsistent allocation (kmalloc) failure in the mei
> > client driver [1] in chromebooks. The crash indicates the driver is
> > requesting for an order 4 allocation that is unavailable at that
> > particular snapshot of the system.
> >
> > I am new to this and do not know the history behind the roundup to
> > order
> > 4 [2]. According to the sources, order 4 allocations are not
> > guaranteed and should be avoided most of the time. And considering the
> > chromebooks limited memory, this may become an expected behavior.
> 
> I don't see how that commit is related to the failure in mei_cl_alloc_cb(), that
> one only rounds the size up to a multiple of four bytes.
> 
> What is the call chain you see in the kernel messages? Is it always the same?

> 
> > Can we have more details on this as to why order 4 allocation is
> > required? Or can we have a lower order allocation request that can be
> > helpful for low memory platforms?

Do we have an log messages for that? Is that during video playback?

> >
> > Some solutions that I explored and weren't applicable/helpful here:
> > 1. using a vmalloc/kvmalloc instead of kmalloc (Due to DMA usage).
> > 2. using a scatter gather list (Would require a lot of rework in the
> > driver and still not sure if that would work as it would require
> > changes in the underlying layer as well) 3. retry mechanism (would
> > help in few instances only).
> > 4. allocating from the DMA pool?
> 
> Those (1, 2 and 4) would have been my suggestions as well ;-) I don't think 4
> helps on x86 machines though, since there is no CMA area (and there should
> not need to be either).
> 
> If this happens during runtime (after the system is alredy fully booted),
> another idea would be to move the allocation to boot time where it is very
> likely to succeed and just never free it again. Whether that works or not
> depends on the exact call chain.
> 
> Allocating 64KB of consecutive pages repeatedly is clearly a problem at
> runtime, but having a single allocation during probe time is not as bad.

Would really helpful if some logs are available.

Thanks
Tomas