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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Date:   Thu, 23 Jul 2020 17:11:42 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        mike.kravetz@...cle.com, 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

On 07/23/20 at 11:46am, Anshuman Khandual wrote:
> 
> 
> On 07/23/2020 08:52 AM, Baoquan He wrote:
> > A customer complained that no message is logged wh	en the number of
> > persistent huge pages is not changed to the exact value written to
> > the sysfs or proc nr_hugepages file.
> > 
> > In the current code, a best effort is made to satisfy requests made
> > via the nr_hugepages file.  However, requests may be only partially
> > satisfied.
> > 
> > Log a message if the code was unsuccessful in fully satisfying a
> > request. This includes both increasing and decreasing the number
> > of persistent huge pages.
> 
> 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().

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.

Thanks
Baoquan