Re: [RFC PATCH 0/3] target: try satisfying memory requests with higher-order allocations

Nicholas A. Bellinger
2012-09-06T01:58:22Z

On Wed, 2012-09-05 at 17:13 +0200, Paolo Bonzini wrote:
> Hi all,
>
> while testing PSCSI I noticed that even requests for a smallish amount
> of data (approximately 700 KB) failed due to an excessive number of
> segments in the request. In fact, using alloc_page resulted in a
> completely fragmented request, with no merging of consecutive pages
> at all.
>
> This patch series fixes this problem by using higher-order allocations
> to build the data scatterlist. The problem is that iscsi assumes that the
> scatterlist consists of single pages, which is not true anymore. So
> patch 2 has to introduce some relatively complicated changes to
> iscsi_map_iovec and iscsi_unmap_iovec.
>

So enabling multi-page per SGL support is a feature that has been
dormant within target core for a long time. It's about time that we
start taking advantage of it again. ;)

> While doing this, I noticed something strange in iscsit_do_crypto_hash_sg.
> Patch 1 adds a warning about it.
>

Mmmmm, looks like a separate bug with DataDigest enabled.

> The approach may be completely wrong and it needs more testing anyway.
> Please review!
>

Adding my comments inline.

Thanks Paolo!

--nab

> Paolo
>
> Paolo Bonzini (3):
> tcm_iscsi: warn on incorrect precondition for iscsit_do_crypto_hash_sg
> tcm_iscsi: support multiple sizes in the scatterlist
> target: try satisfying memory requests with contiguous blocks
>
> drivers/target/iscsi/iscsi_target.c | 106 +++++++++++++++++++++++++-----
> drivers/target/iscsi/iscsi_target_core.h | 2 +-
> drivers/target/target_core_transport.c | 58 ++++++++++++++---
> 3 files changed, 138 insertions(+), 28 deletions(-)
>
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