linux-kernel - Re: [HPDD-discuss] [PATCH 2/11] Staging: lustre: fld: Use kzalloc and kfree

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Date:	Fri, 1 May 2015 22:47:29 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	"Simmons, James A." <simmonsja@...l.gov>
Cc:	'Julia Lawall' <julia.lawall@...6.fr>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Oleg Drokin <oleg.drokin@...el.com>,
	"HPDD-discuss@...ts.01.org" <HPDD-discuss@...1.01.org>
Subject: Re: [HPDD-discuss] [PATCH 2/11] Staging: lustre: fld: Use kzalloc
 and kfree

On Fri, May 01, 2015 at 08:18:56PM +0000, Simmons, James A. wrote:
> >> >From: Julia Lawall <Julia.Lawall@...6.fr>
> >> >
> >> >Replace OBD_ALLOC, OBD_ALLOC_WAIT, OBD_ALLOC_PTR, and OBD_ALLOC_PTR_WAIT by
> >> >kalloc/kcalloc, and OBD_FREE and OBD_FREE_PTR by kfree.
> >> 
> >> Nak: James Simmons <jsimmons@...radead.org>
> >> 
> >> A simple replace will not work. The OBD_ALLOC and OBD_FREE functions allocate memory
> >> anywhere from one page to 4MB in size. You can't use kmalloc for the 4MB allocations.
> >> Currently lustre uses  a 4 page water mark to determine if we allocate using vmalloc. Even
> >> using kmalloc for 4 pages has shown high failure rates on some systems. It gets even more
> >> messy with 64K page systems like ppc64 boxes. Now I'm not suggesting to port the larger
> >> allocations to vmalloc either since issues have been founded with using vmalloc. For example
> >> when using large stripe count files the MDS rpc generated crosses the 4 page line and vmalloc
> >> is used. Using vmalloc caused a global spinlock to be taken which causes meta data operations
> >> to serialized on the MDS servers.
> >
> >It's not the LARGE functions that do the switching?  For example OBD_ALLOC 
> >ends up at  __OBD_MALLOC_VERBOSE, which as far as I can see calls kmalloc 
> >(with __GFP_ZERO, and hance the use of kzalloc).
> 
> Yes the LARGE functions do the switching. I was expecting also patches to remove the 
> OBD_ALLOC_LARGE functions as well which is not the case here.  I do have one question still. The
> macro __OBD_MALLOC_VERBOSE allowed the ability to simulate memory allocation failures at
> a certain percentage rate. Does something exist in the kernel to duplicate that functionality?

Yes, no need for lustre to duplicate yet-another-thing the kernel
already provides :)

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