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

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Date:	Fri, 1 May 2015 17:38:49 +0000
From:	"Simmons, James A." <simmonsja@...l.gov>
To:	'Julia Lawall' <Julia.Lawall@...6.fr>,
	Oleg Drokin <oleg.drokin@...el.com>
CC:	"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@...ts.01.org>
Subject: RE: [HPDD-discuss] [PATCH 2/11] Staging: lustre: fld: Use kzalloc and
	kfree

>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.

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