linux-kernel - Re: [PATCH v2 4/4] mm/hugetl.c: warn out if expected count of huge pages adjustment is not achieved

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Message-ID: <20200811021152.GW14854@MiWiFi-R3L-srv>
Date:   Tue, 11 Aug 2020 10:11:52 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, david@...hat.com,
        akpm@...ux-foundation.org
Subject: Re: [PATCH v2 4/4] mm/hugetl.c: warn out if expected count of huge
 pages adjustment is not achieved

Hi Mike,

On 07/23/20 at 11:21am, Mike Kravetz wrote:
> On 7/23/20 2:11 AM, Baoquan He wrote:
...
> >> But is kernel expected to warn for all such situations where the user
> >> requested resources could not be allocated completely ? Otherwise, it
> >> does not make sense to add an warning for just one such situation.
> > 
> > It's not for just one such situation, we have already had one to warn
> > out in mm/hugetlb.c, please check hugetlb_hstate_alloc_pages().
> 
> Those are a little different in that they are warnings based on kernel
> command line parameters.
> 
> > As Mike said, in one time of persistent huge page number setting,
> > comparing the old value with the new vlaue is good enough for customer
> > to get the information. However, if customer want to detect and analyze
> > previous setting failure, logging message will be helpful. So I think
> > logging the failure or partial success makes sense.
> 
> I can understand the argument against adding a new warning for this.
> You could even argue that this condition has existed since the time
> hugetlb was added to the kernel which was long ago.  And, nobody has
> complained enough to add a warning.  I have even heard of a sysadmin
> practice of asking for a ridiculously large amount of hugetlb pages
> just so that the kernel will allocate as many as possible.  They do
> not 'expect' to get the ridiculous amount they asked for.  In such
> cases, this will be a new warning in their log.
> 
> As mentioned in a previous e-mail, when one sets nr_hugepages by writing
> to the sysfs or proc file, one needs to read the file to determine if the
> number of requested pages were actually allocated.  Anyone who does not
> do this is just asking for trouble.  Yet, I imagine that it may happen.
> 
> To be honest, I do not see this log message as something that would be
> helpful to end users.  Rather, I could see this as being useful to support
> people.  Support always asks for system logs and this could point out a
> possible issue with hugetlb usage.
> 
> I do not feel strongly one way or another about adding the warning.  Since
> it is fairly trivial and could help diagnose issues I am in favor of adding
> it.  If people feel strongly that it should not be added, I am open to
> those arguments.

Ping!

It's been a while, seems no objection to log the message. Do you
consider accepting this patch or offering an Ack?

Thanks
Baoquan