[dm-devel] The DM_BUFIO_HASH_BITS is defined as 20, any plan to make it flexible?
Joe Thornber
thornber at redhat.com
Wed Dec 3 14:19:22 UTC 2014
On Tue, Dec 02, 2014 at 09:00:17AM -0500, Mike Snitzer wrote:
> On Tue, Dec 02 2014 at 3:43am -0500,
> zhangxiao <xiao.zhang at windriver.com> wrote:
>
> > Hi Experts,
> >
> > See drivers/md/dm-bufio.c as below:
> > 50 /*
> > 51 * Buffer hash
> > 52 */
> > 53 #define DM_BUFIO_HASH_BITS 20
> > 54 #define DM_BUFIO_HASH(block) \
> > 55 ((((block) >> DM_BUFIO_HASH_BITS) ^ (block)) & \
> > 56 ((1 << DM_BUFIO_HASH_BITS) - 1))
> > "drivers/md/dm-bufio.c" 1854L, 45375C
> >
> > DM_BUFIO_HASH_BITS was defined as 20 and it maybe not fit for some
> > use case with limited resources. Do we have any plan to make it more
> > flexible? Like module parameter or something else?
>
> No immediate plans.
That hash table has been replaced with a red/black tree.
https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-for-3.19&id=4e420c452b11edf9d510c8180ac66f529e5b6206
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