Re: [PATCH] Use MAP_HUGETLB where supported (v3)

On Thu, Oct 24, 2013 at 1:00 PM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> On 2013-10-24 16:06:19 +0300, Heikki Linnakangas wrote:
>> On 24.10.2013 09:03, Abhijit Menon-Sen wrote:
>> >One open question is what to do about rounding up the size. It should
>> >not be necessary, but for the fairly recent bug described at the link
>> >in the comment (https://bugzilla.kernel.org/show_bug.cgi?id=56881) I
>> >tried it without the rounding-up, and it fails on Ubuntu's 3.5.0-28
>> >kernel (mmap returns EINVAL).
>>
>> Let's get rid of the rounding. It's clearly a kernel bug, and it shouldn't
>> be our business to add workarounds for any kernel bug out there. And the
>> worst that will happen if you're running a buggy kernel version is that you
>> fall back to not using huge pages (assuming huge_tlb_pages=try).
>
> But it's a range of relatively popular kernels, that will stay around
> for a good while. So I am hesitant to just not do anything about it. The
> directory scanning code isn't that bad imo.
>
> Either way:
> I think we should log when we tried to use hugepages but fell back to
> plain mmap, currently it's hard to see whether they are used.

Logging it might be a good idea, but suppose the systems been running
for 6 months and you don't have the startup logs. Might be a good way
to have an easy way to discover later what happened back then.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company