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Date: Mon, 17 Nov 2008 10:13:46 +0530 From: Balbir Singh <balbir@...ux.vnet.ibm.com> To: Dave Airlie <airlied@...il.com> CC: Arjan van de Ven <arjan@...radead.org>, David Miller <davem@...emloft.net>, laijs@...fujitsu.com, akpm@...ux-foundation.org, menage@...gle.com, kamezawa.hiroyu@...fujitsu.com, jens.axboe@...cle.com, jack@...e.cz, jes@....com, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/7] mm: introduce simple_malloc()/simple_free() Dave Airlie wrote: > On Mon, Nov 17, 2008 at 4:57 AM, Arjan van de Ven <arjan@...radead.org> wrote: >> On Sun, 16 Nov 2008 00:19:26 -0800 (PST) >> David Miller <davem@...emloft.net> wrote: >> >>> From: Arjan van de Ven <arjan@...radead.org> >>> Date: Sat, 15 Nov 2008 20:52:29 -0800 >>> >>>> On Sun, 16 Nov 2008 12:33:15 +0800 >>>> Lai Jiangshan <laijs@...fujitsu.com> wrote: >>>> >>>>> some subsystem needs vmalloc() when required memory is large. >>>>> but current kernel has not APIs for this requirement. >>>>> this patch introduces simple_malloc() and simple_free(). >>>> I kinda really don't like this approach. vmalloc() (and especially, >>>> vfree()) is a really expensive operation, and vmalloc()'d memory is >>>> also slower (due to tlb pressure). Realistically, people should try >>>> hard to use small datastructure instead.... >>> This is happening in many places, already, for good reason. >>> >>> There are lots of places where we can't (core hash tables, etc.) and >>> we want NUMA spreading and reliable allocation, and thus vmalloc it >>> is. >> vmalloc() isn't 100% evil; for truely long term stuff it's sometimes a >> quite reasonable solution. >> >> There are some issues with it still: the vmalloc() space is shared >> with ioremap, modules and others and it's not all that big on 32 bit; on >> x86 you could well end up with only 64Mb total (after taking out the >> various ioremap's etc). >> >> Yes there's places where it's then totally fine to dip into this space >> at boot/init time. You mention a few very good users. >> (There's still the tlb miss cost on use but on modern cpus a tlb miss >> is actually quite cheap) >> >> But this doesn't make vmalloc() the magic bullet that solves the "oh >> Linux can't allocate large chunks of memory" problem. Specifically in >> driver space for things that get ported from other OSes. > > So we keep the duplicated code? or we just audit new callers.... I > think this patch > makes it easier to spot new callers doing something stupid. As davem > said we duplicate > this code all over the place, so for that reason along a simple > wrapper makes things a lot > easier, and also possibly a lot easier to change in the future to a > new non-sucky API. > > So I'm all for it maybe with a non simple name. Yes, tracking vmalloc() spillage all over the place is harder than using one abstraction and fixing that appropriately if needed (specially for 32 bit systems). -- Balbir -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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