How to avoid or reduce GFP_ATOMIC allocation failed

How to avoid or reduce GFP_ATOMIC allocation failed

[wuzhouhui]

Hi,

I check kernel code and found that GFP_ATOMIC allocation will
use emergency pool and maybe failed if emergency pool is not
enough. And GFP_ATOMIC doesn't trigger reclaim (because of
ATOMIC) even if there are a lot of page caches. So my question
is how to avoid or reduce GFP_ATOMIC allocation failed if there
are enough reclaimable memory? Is there some kernel parameters
can be configured?

Thanks.
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Re: How to avoid or reduce GFP_ATOMIC allocation failed

[Greg KH]

On Fri, Mar 08, 2019 at 01:37:26PM +0800, wuzhouhui wrote:
> Hi,
> 
> I check kernel code and found that GFP_ATOMIC allocation will
> use emergency pool and maybe failed if emergency pool is not
> enough. And GFP_ATOMIC doesn't trigger reclaim (because of
> ATOMIC) even if there are a lot of page caches. So my question
> is how to avoid or reduce GFP_ATOMIC allocation failed if there
> are enough reclaimable memory? Is there some kernel parameters
> can be configured?

Have you seen the ATOMIC pools be used up and not able to be reclaimed
in real-world usages?  If so, I'm sure the mm developers would love to
hear from you about this as I really do not think that is a situation
that can happen easily, if at all.

And no, I do not think there are any such parameters, the kernel should
be self-tuning for things like this.

thanks,

greg k-h

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Re: Re: How to avoid or reduce GFP_ATOMIC allocation failed

[wuzhouhui]

> -----Original Messages-----
> From: "Greg KH" <greg@kroah.com>
> Sent Time: 2019-03-08 15:21:52 (Friday)
> To: wuzhouhui <wuzhouhui14@mails.ucas.ac.cn>
> Cc: kernelnewbies@kernelnewbies.org
> Subject: Re: How to avoid or reduce GFP_ATOMIC allocation failed
> 
> On Fri, Mar 08, 2019 at 01:37:26PM +0800, wuzhouhui wrote:
> > Hi,
> > 
> > I check kernel code and found that GFP_ATOMIC allocation will
> > use emergency pool and maybe failed if emergency pool is not
> > enough. And GFP_ATOMIC doesn't trigger reclaim (because of
> > ATOMIC) even if there are a lot of page caches. So my question
> > is how to avoid or reduce GFP_ATOMIC allocation failed if there
> > are enough reclaimable memory? Is there some kernel parameters
> > can be configured?
> 
> Have you seen the ATOMIC pools be used up and not able to be reclaimed
> in real-world usages?  If so, I'm sure the mm developers would love to

No, I haven't seen this scenario. But I encountered the similar issue
with [1] (order is 5 in my scenario), and this issue is not resolved for
now.

Thanks.

[1] https://stackoverflow.com/questions/53936183/linux-disk-cache-and-kmalloc-with-gfp-atomic#

> hear from you about this as I really do not think that is a situation
> that can happen easily, if at all.
> 
> And no, I do not think there are any such parameters, the kernel should
> be self-tuning for things like this.
> 
> thanks,
> 
> greg k-h
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Re: Re: How to avoid or reduce GFP_ATOMIC allocation failed

[greg kh]

On Fri, Mar 08, 2019 at 03:34:18PM +0800, wuzhouhui wrote:
> > -----Original Messages-----
> > From: "Greg KH" <greg@kroah.com>
> > Sent Time: 2019-03-08 15:21:52 (Friday)
> > To: wuzhouhui <wuzhouhui14@mails.ucas.ac.cn>
> > Cc: kernelnewbies@kernelnewbies.org
> > Subject: Re: How to avoid or reduce GFP_ATOMIC allocation failed
> > 
> > On Fri, Mar 08, 2019 at 01:37:26PM +0800, wuzhouhui wrote:
> > > Hi,
> > > 
> > > I check kernel code and found that GFP_ATOMIC allocation will
> > > use emergency pool and maybe failed if emergency pool is not
> > > enough. And GFP_ATOMIC doesn't trigger reclaim (because of
> > > ATOMIC) even if there are a lot of page caches. So my question
> > > is how to avoid or reduce GFP_ATOMIC allocation failed if there
> > > are enough reclaimable memory? Is there some kernel parameters
> > > can be configured?
> > 
> > Have you seen the ATOMIC pools be used up and not able to be reclaimed
> > in real-world usages?  If so, I'm sure the mm developers would love to
> 
> No, I haven't seen this scenario. But I encountered the similar issue
> with [1] (order is 5 in my scenario), and this issue is not resolved for
> now.

Please work with the company that created your out-of-tree kernel
networking code as it sounds like they do not know how to properly
handle this type of problem :)

good luck!

greg k-h

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