Re: Use of kmalloc vs vmalloc in ext4?

[Michael Rubin <mrubin@google.com>]

Anyone have any comments? Or historical reasons? We operate with some
constrained memory situations, and were wondering if a patch to move
from kmalloc to vmalloc would be well received.

mrubin

On Wed, Mar 11, 2009 at 7:32 AM, Curt Wohlgemuth <curtw@google.com> wrote:
> I've been running various tests of ext4 partitions lately, and have
> found that with very low memory situations, I'm getting intermittent
> mount failures due to ENOMEM from ext4_mb_init() and
> ext4_fill_flex_info() .  Here's a typical dmesg from the latter:
>
>          EXT4-fs: not enough memory for 8198 flex groups
>          EXT4-fs: unable to initialize flex_bg meta info!
>
> This is from a kzalloc() call of size ~64k .  I think the
> ext4_mb_init() calls to kmalloc() and alloc_percpu() are even smaller.
>
> I was wondering why all the code in ext4 (and ext[23], for that
> matter) uses kmalloc() and friends instead of vmalloc(), at least
> where it's safe; is it just for performance reasons?
>
> I've seen the above errors when I do a mount -a, causing several
> partitions to be mounted; I can usually mount the failed ones by hand
> right afterwards, but this is a big difference for us, in our
> environment, compared to, say, ext2 partitions.
>
> Thanks,
> Curt
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