Re: [dpdk-dev] [PATCH 2/2] memalloc: keep in mind a failed MAP_FIXED mmap may still perform an unmap

["Stojaczyk, DariuszX" <dariuszx.stojaczyk@intel.com>]

> -----Original Message-----
> From: Burakov, Anatoly
> Sent: Friday, June 1, 2018 1:09 PM
> To: Stojaczyk, DariuszX <dariuszx.stojaczyk@intel.com>; dev@dpdk.org
> Subject: Re: [PATCH 2/2] memalloc: keep in mind a failed MAP_FIXED
> mmap may still perform an unmap
> 
> On 01-Jun-18 1:51 PM, Dariusz Stojaczyk wrote:
> > This isn't documented in the manuals, but a failed mmap(...,
> > MAP_FIXED) may still unmap overlapping regions. In such case, we need
> > to remap these regions back into our address space to ensure mem
> > contiguity.
> > We do it unconditionally now on mmap failure just to be safe.
> >
> > Verified on Linux 4.9.0-4-amd64. I was getting ENOMEM when trying to
> > map in hugetlbfs with no space left, but the previous anonymous
> > mapping was still being removed.
> >
> > Signed-off-by: Dariusz Stojaczyk <dariuszx.stojaczyk@intel.com>
> > ---
> 
> Does this also happen with other error values?

The man pages aren't clear on this. It could. I know this patch only remaps the region if errrno == ENOMEM, but we could remap it unconditionally after each failed mmap just as well.  It won't hurt if we remap a region unnecessarily. This was my original intent, but apparently I didn't fully commit my changes before publishing patches here. Uhh, sorry.

D.

> 
> --
> Thanks,
> Anatoly