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SubjectRe: [PATCH 00/20] staging: lustre: convert to rhashtable

> libcfs in lustre has a resizeable hashtable.
> Linux already has a resizeable hashtable, rhashtable, which is better
> is most metrics. See https://lwn.net/Articles/751374/ in a few days
> for an introduction to rhashtable.

Thansk for starting this work. I was think about cleaning the libcfs
hash but your port to rhashtables is way better. How did you gather
metrics to see that rhashtable was better than libcfs hash?

> This series converts lustre to use rhashtable. This affects several
> different tables, and each is different is various ways.
>
> There are two outstanding issues. One is that a bug in rhashtable
> means that we cannot enable auto-shrinking in one of the tables. That
> is documented as appropriate and should be fixed soon.
>
> The other is that rhashtable has an atomic_t which counts the elements
> in a hash table. At least one table in lustre went to some trouble to
> avoid any table-wide atomics, so that could lead to a regression.
> I'm hoping that rhashtable can be enhanced with the option of a
> per-cpu counter, or similar.
>

This doesn't sound quite ready to land just yet. This will have to do some
soak testing and a larger scope of test to make sure no new regressions
happen. Believe me I did work to make lustre work better on tickless
systems, which I'm preparing for the linux client, and small changes could
break things in interesting ways. I will port the rhashtable change to the
Intel developement branch and get people more familar with the hash code
to look at it.

> I have enabled automatic shrinking on all tables where it makes sense
> and doesn't trigger the bug. I have also removed all hints concerning
> min/max size - I cannot see how these could be useful.
>
> The dump_pgcache debugfs file provided some interesting challenges. I
> think I have cleaned it up enough so that it all makes sense. An
> extra pair of eyes examining that code in particular would be
> appreciated.
>
> This series passes all the same tests that pass before the patches are
> applied.
>
> Thanks,
> NeilBrown
>
>
> ---
>
> NeilBrown (20):
> staging: lustre: ptlrpc: convert conn_hash to rhashtable
> staging: lustre: convert lov_pool to use rhashtable
> staging: lustre: convert obd uuid hash to rhashtable
> staging: lustre: convert osc_quota hash to rhashtable
> staging: lustre: separate buckets from ldlm hash table
> staging: lustre: ldlm: add a counter to the per-namespace data
> staging: lustre: ldlm: store name directly in namespace.
> staging: lustre: simplify ldlm_ns_hash_defs[]
> staging: lustre: convert ldlm_resource hash to rhashtable.
> staging: lustre: make struct lu_site_bkt_data private
> staging: lustre: lu_object: discard extra lru count.
> staging: lustre: lu_object: factor out extra per-bucket data
> staging: lustre: lu_object: move retry logic inside htable_lookup
> staging: lustre: fold lu_object_new() into lu_object_find_at()
> staging: lustre: llite: use more private data in dump_pgcache
> staging: lustre: llite: remove redundant lookup in dump_pgcache
> staging: lustre: use call_rcu() to free lu_object_headers
> staging: lustre: change how "dump_page_cache" walks a hash table
> staging: lustre: convert lu_object cache to rhashtable
> staging: lustre: remove cfs_hash resizeable hashtable implementation.
>
>
> .../staging/lustre/include/linux/libcfs/libcfs.h | 1
> .../lustre/include/linux/libcfs/libcfs_hash.h | 866 --------
> drivers/staging/lustre/lnet/libcfs/Makefile | 2
> drivers/staging/lustre/lnet/libcfs/hash.c | 2064 --------------------
> drivers/staging/lustre/lnet/libcfs/module.c | 12
> drivers/staging/lustre/lustre/include/lu_object.h | 55 -
> drivers/staging/lustre/lustre/include/lustre_dlm.h | 19
> .../staging/lustre/lustre/include/lustre_export.h | 2
> drivers/staging/lustre/lustre/include/lustre_net.h | 4
> drivers/staging/lustre/lustre/include/obd.h | 11
> .../staging/lustre/lustre/include/obd_support.h | 9
> drivers/staging/lustre/lustre/ldlm/ldlm_request.c | 31
> drivers/staging/lustre/lustre/ldlm/ldlm_resource.c | 370 +---
> drivers/staging/lustre/lustre/llite/lcommon_cl.c | 8
> drivers/staging/lustre/lustre/llite/vvp_dev.c | 332 +--
> drivers/staging/lustre/lustre/llite/vvp_object.c | 9
> drivers/staging/lustre/lustre/lov/lov_internal.h | 11
> drivers/staging/lustre/lustre/lov/lov_obd.c | 12
> drivers/staging/lustre/lustre/lov/lov_object.c | 8
> drivers/staging/lustre/lustre/lov/lov_pool.c | 159 +-
> drivers/staging/lustre/lustre/lov/lovsub_object.c | 9
> drivers/staging/lustre/lustre/obdclass/genops.c | 34
> drivers/staging/lustre/lustre/obdclass/lu_object.c | 564 ++---
> .../staging/lustre/lustre/obdclass/obd_config.c | 161 +-
> .../staging/lustre/lustre/obdecho/echo_client.c | 8
> drivers/staging/lustre/lustre/osc/osc_internal.h | 5
> drivers/staging/lustre/lustre/osc/osc_quota.c | 136 -
> drivers/staging/lustre/lustre/osc/osc_request.c | 12
> drivers/staging/lustre/lustre/ptlrpc/connection.c | 164 +-
> 29 files changed, 870 insertions(+), 4208 deletions(-)
> delete mode 100644 drivers/staging/lustre/include/linux/libcfs/libcfs_hash.h
> delete mode 100644 drivers/staging/lustre/lnet/libcfs/hash.c
>
> --
> Signature
>
>

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