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

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Message-ID: <alpine.DEB.2.02.1505011945350.2092@localhost6.localdomain6>
Date:	Fri, 1 May 2015 19:48:20 +0200 (CEST)
From:	Julia Lawall <julia.lawall@...6.fr>
To:	"Simmons, James A." <simmonsja@...l.gov>
cc:	'Julia Lawall' <Julia.Lawall@...6.fr>,
	Oleg Drokin <oleg.drokin@...el.com>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"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, 1 May 2015, 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).

julia
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