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From: "Philippe Mathieu-Daudé" <philmd@redhat.com>
To: David Hildenbrand <david@redhat.com>,
	Peter Maydell <peter.maydell@linaro.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>,
	Peter Xu <peterx@redhat.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Igor Mammedov <imammedo@redhat.com>,
	Bin Meng <bmeng.cn@gmail.com>
Subject: Re: [PATCH] softmmu/physmem: Improve guest memory allocation failure error message
Date: Mon, 23 Aug 2021 12:12:47 +0200	[thread overview]
Message-ID: <1a63c2d2-7420-5fc1-1023-0504a67dc40b@redhat.com> (raw)
In-Reply-To: <6165f86e-1ce7-d178-1f5c-4b3c5110f0c1@redhat.com>

On 8/23/21 11:29 AM, David Hildenbrand wrote:
> On 23.08.21 11:23, Peter Maydell wrote:
>> On Mon, 23 Aug 2021 at 09:40, David Hildenbrand <david@redhat.com> wrote:
>>> Not opposed to printing the size, although I doubt that it will really
>>> stop similar questions/problems getting raised.
>>
>> The case that triggered this was somebody thinking
>> -m took a byte count, so very likely that an error message
>> saying "you tried to allocate 38TB" would have made their
>> mistake clear in a way that just "allocation failed" did not.
>> It also means that if a future user asks us for help then
>> we can look at the error message and immediately tell them
>> the problem, rather than going "hmm, what are all the possible
>> ways that allocation might have failed" and going off down
>> rabbitholes like VM overcommit settings...
> 
> We've had similar issues recently where Linux memory overcommit handling
> rejected the allocation -- and the user was well aware about the actual
> size. You won't be able to catch such reports, because people don't
> understand how Linux memory overcommit handling works or was configured.
> 
> "I have 3 GiB of free memory, why can't I create a 3 GiB VM". "I have 3
> GiB of RAM, why can't I create a 3 GiB VM even if it won't make use of
> all 3 GiB of memory".
> 
> Thus my comment, it will only stop very basic usage issues. And I agree
> that looking at the error *might* help. It didn't help for the cases I
> just described, because we need much more system information to make a
> guess what the user error actually is.

Is it possible to get the maximal overcommitable amount on Linux?



  reply	other threads:[~2021-08-23 10:13 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-20 15:52 [PATCH] softmmu/physmem: Improve guest memory allocation failure error message Philippe Mathieu-Daudé
2021-08-20 15:53 ` David Hildenbrand
2021-08-20 16:00   ` Philippe Mathieu-Daudé
2021-08-20 16:40     ` Igor Mammedov
2021-08-20 16:59       ` Philippe Mathieu-Daudé
2021-08-20 17:13         ` Peter Maydell
2021-08-23  8:38     ` David Hildenbrand
2021-08-23  9:23       ` Peter Maydell
2021-08-23  9:29         ` David Hildenbrand
2021-08-23 10:12           ` Philippe Mathieu-Daudé [this message]
2021-08-23 10:24             ` David Hildenbrand
2021-08-23 10:34               ` Philippe Mathieu-Daudé
2021-08-23 19:27                 ` David Hildenbrand
2021-08-24  8:37                   ` Dr. David Alan Gilbert
2021-08-24  8:53                     ` David Hildenbrand
2021-08-24 11:42                     ` Igor Mammedov
2021-08-20 20:31 ` Peter Xu
2021-08-21 10:01 ` Bin Meng
2021-08-21 10:41   ` Peter Maydell
2021-08-21 13:32   ` Philippe Mathieu-Daudé

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