linux-kernel - Re: [PATCH 3/3] Quick vmalloc vs kmalloc fix to the case where array size is too large

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Message-ID: <2f86c2480907141430u314f8987s857bdaa229d6e482@mail.gmail.com>
Date:	Tue, 14 Jul 2009 14:30:28 -0700
From:	Benjamin Blum <bblum@...gle.com>
To:	Paul Menage <menage@...gle.com>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 3/3] Quick vmalloc vs kmalloc fix to the case where array 
	size is too large

Indeed.

Alternatively, I could make it case on KMALLOC_MAX_SIZE as follows:

if (size > KMALLOC_MAX_SIZE) {
    /* use vmalloc directly */
} else {
    /* try kmalloc, and, expecting fragmentation, if that fails, use vmalloc */
}

As the free wrapper uses is_vmalloc_addr, it'd work fine and be able
to decide for a certain range of sizes whether kmalloc or vmalloc is
appropriate.

On Tue, Jul 14, 2009 at 10:50 AM, Paul Menage<menage@...gle.com> wrote:
> On Tue, Jul 14, 2009 at 10:47 AM, Dave Hansen<dave@...ux.vnet.ibm.com> wrote:
>>
>> How big were those allocations that were failing?  The code made it
>> appear that order-2 (PAGE_SIZE*4) allocations were failing.  That's a
>> bit lower than I'd expect the page allocator to start failing.
>
> I think it depends on how much fragmentation you've got.
>
> We've seen it fail for cpusets with (I guess) hundreds or thousands of threads.
>
> Paul
>
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