From: Mike Snitzer <snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> To: Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org> Cc: Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>, linux-xfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-raid-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, darrick.wong-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, colyli-l3A5Bk7waGM@public.gmane.org, linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, clm-b10kYP2dOMg@public.gmane.org, neilb-IBi9RG/b67k@public.gmane.org, bacik-b10kYP2dOMg@public.gmane.org, Kent Overstreet <kent.overstreet-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, linux-btrfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, drbd-dev-cunTk1MwBs8qoQakbn7OcQ@public.gmane.org Subject: Re: [PATCH 00/13] convert block layer to bioset_init()/mempool_init() Date: Tue, 22 May 2018 15:09:34 -0400 [thread overview] Message-ID: <20180522190933.GA25904@redhat.com> (raw) In-Reply-To: <20180522064118.GA18704-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org> On Tue, May 22 2018 at 2:41am -0400, Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org> wrote: > On Mon, May 21, 2018 at 07:38:55PM -0400, Kent Overstreet wrote: > > On Mon, May 21, 2018 at 02:24:32PM -0400, Mike Snitzer wrote: > > > Every single data structure change in this series should be reviewed for > > > unforeseen alignment consequences. Jens seemed to say that is > > > worthwhile. Not sure if he'll do it or we divide it up. If we divide > > > it up a temp topic branch should be published for others to inspect. > > > > > > Could be alignment hasn't been a historic concern for a bunch of the > > > data structures changed in this series.. if so then all we can do is fix > > > up any obvious potential for false sharing. > > > > Honestly, I almost never worry about alignment... the very few times I do care, > > I use __cacheline_aligned_in_smp. > > And that generally is the right stratgey. If Mike really doesn't want > a change we can just open code the kmalloc for the bio set there, the > important point is that we should not keep the old API around for no > good reason. Again, I never said I didn't want these changes. I just thought it worthwhile to mention the potential for alignment quirks arising. Reality is false sharing is quite uncommon. So my concern was/is pretty niche and unlikely to be applicable. That said, I did take the opportunity to look at all the DM structures that were modified. The bio_set and mempool_t structs are so large that they span multiple cachelines as is. So I focused on eliminating unnecessary spanning of cachelines (by non-bio_set and non-mempool_t members) and eliminated most holes in DM structs. This is the result: http://people.redhat.com/msnitzer/dm-4.18-struct-reorg/ Compare before.txt vs after_kent.txt vs after_mike.txt Nothing staggering or special. Just something I'll add once Kent's latest changes land. But, I also eliminated 2 4-byte holes in struct bio_set, Jens please feel free to pick this up (if you think it useful): From: Mike Snitzer <snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Subject: [PATCH] block: eliminate 2 4-byte holes in bio_set structure Signed-off-by: Mike Snitzer <snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> --- include/linux/bio.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/bio.h b/include/linux/bio.h index 5e472fc..e6fc692 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -735,7 +735,6 @@ static inline void bio_inc_remaining(struct bio *bio) struct bio_set { struct kmem_cache *bio_slab; - unsigned int front_pad; mempool_t bio_pool; mempool_t bvec_pool; @@ -743,6 +742,7 @@ struct bio_set { mempool_t bio_integrity_pool; mempool_t bvec_integrity_pool; #endif + unsigned int front_pad; /* * Deadlock avoidance for stacking block drivers: see comments in
WARNING: multiple messages have this Message-ID (diff)
From: Mike Snitzer <snitzer@redhat.com> To: Christoph Hellwig <hch@infradead.org> Cc: Kent Overstreet <kent.overstreet@gmail.com>, Jens Axboe <axboe@kernel.dk>, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, colyli@suse.de, darrick.wong@oracle.com, clm@fb.com, bacik@fb.com, linux-xfs@vger.kernel.org, drbd-dev@lists.linbit.com, linux-btrfs@vger.kernel.org, linux-raid@vger.kernel.org, neilb@suse.com Subject: Re: [PATCH 00/13] convert block layer to bioset_init()/mempool_init() Date: Tue, 22 May 2018 15:09:34 -0400 [thread overview] Message-ID: <20180522190933.GA25904@redhat.com> (raw) In-Reply-To: <20180522064118.GA18704@infradead.org> On Tue, May 22 2018 at 2:41am -0400, Christoph Hellwig <hch@infradead.org> wrote: > On Mon, May 21, 2018 at 07:38:55PM -0400, Kent Overstreet wrote: > > On Mon, May 21, 2018 at 02:24:32PM -0400, Mike Snitzer wrote: > > > Every single data structure change in this series should be reviewed for > > > unforeseen alignment consequences. Jens seemed to say that is > > > worthwhile. Not sure if he'll do it or we divide it up. If we divide > > > it up a temp topic branch should be published for others to inspect. > > > > > > Could be alignment hasn't been a historic concern for a bunch of the > > > data structures changed in this series.. if so then all we can do is fix > > > up any obvious potential for false sharing. > > > > Honestly, I almost never worry about alignment... the very few times I do care, > > I use __cacheline_aligned_in_smp. > > And that generally is the right stratgey. If Mike really doesn't want > a change we can just open code the kmalloc for the bio set there, the > important point is that we should not keep the old API around for no > good reason. Again, I never said I didn't want these changes. I just thought it worthwhile to mention the potential for alignment quirks arising. Reality is false sharing is quite uncommon. So my concern was/is pretty niche and unlikely to be applicable. That said, I did take the opportunity to look at all the DM structures that were modified. The bio_set and mempool_t structs are so large that they span multiple cachelines as is. So I focused on eliminating unnecessary spanning of cachelines (by non-bio_set and non-mempool_t members) and eliminated most holes in DM structs. This is the result: http://people.redhat.com/msnitzer/dm-4.18-struct-reorg/ Compare before.txt vs after_kent.txt vs after_mike.txt Nothing staggering or special. Just something I'll add once Kent's latest changes land. But, I also eliminated 2 4-byte holes in struct bio_set, Jens please feel free to pick this up (if you think it useful): From: Mike Snitzer <snitzer@redhat.com> Subject: [PATCH] block: eliminate 2 4-byte holes in bio_set structure Signed-off-by: Mike Snitzer <snitzer@redhat.com> --- include/linux/bio.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/bio.h b/include/linux/bio.h index 5e472fc..e6fc692 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -735,7 +735,6 @@ static inline void bio_inc_remaining(struct bio *bio) struct bio_set { struct kmem_cache *bio_slab; - unsigned int front_pad; mempool_t bio_pool; mempool_t bvec_pool; @@ -743,6 +742,7 @@ struct bio_set { mempool_t bio_integrity_pool; mempool_t bvec_integrity_pool; #endif + unsigned int front_pad; /* * Deadlock avoidance for stacking block drivers: see comments in
next prev parent reply other threads:[~2018-05-22 19:09 UTC|newest] Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-05-20 22:25 [PATCH 00/13] convert block layer to bioset_init()/mempool_init() Kent Overstreet 2018-05-20 22:25 ` [PATCH 01/12] block: convert bounce, q->bio_split " Kent Overstreet 2018-05-22 10:08 ` Christoph Hellwig 2018-05-20 22:25 ` [PATCH 02/12] drbd: convert " Kent Overstreet 2018-05-20 22:25 ` [PATCH 03/12] pktcdvd: " Kent Overstreet 2018-05-20 22:25 ` [PATCH 04/12] lightnvm: " Kent Overstreet 2018-05-22 10:10 ` Javier Gonzalez 2018-05-20 22:25 ` [PATCH 05/12] bcache: " Kent Overstreet 2018-05-21 3:58 ` Coly Li 2018-05-20 22:25 ` [PATCH 06/12] md: " Kent Overstreet 2018-06-01 10:51 ` Arnd Bergmann 2018-05-20 22:25 ` [PATCH 07/12] dm: " Kent Overstreet [not found] ` <20180520222558.7053-8-kent.overstreet-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> 2018-05-30 19:27 ` Mike Snitzer 2018-05-30 19:27 ` Mike Snitzer 2018-05-20 22:25 ` [PATCH 08/12] target: " Kent Overstreet 2018-05-22 10:09 ` Christoph Hellwig 2018-05-20 22:25 ` [PATCH 09/12] fs: convert block_dev.c to bioset_init() Kent Overstreet 2018-05-22 10:09 ` Christoph Hellwig 2018-05-20 22:25 ` [PATCH 10/12] btrfs: convert to bioset_init()/mempool_init() Kent Overstreet 2018-05-30 21:30 ` Chris Mason 2018-05-30 21:30 ` Chris Mason 2018-05-20 22:25 ` [PATCH 11/12] xfs: " Kent Overstreet 2018-05-21 18:39 ` Darrick J. Wong [not found] ` <20180520222558.7053-12-kent.overstreet-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> 2018-05-22 10:10 ` Christoph Hellwig 2018-05-22 10:10 ` Christoph Hellwig 2018-05-20 22:25 ` [PATCH 12/12] block: Drop bioset_create() Kent Overstreet 2018-05-22 10:10 ` Christoph Hellwig 2018-05-20 23:08 ` [PATCH 00/13] convert block layer to bioset_init()/mempool_init() NeilBrown 2018-05-20 23:08 ` NeilBrown 2018-05-20 23:11 ` Kent Overstreet [not found] ` <20180520222558.7053-1-kent.overstreet-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> 2018-05-21 14:03 ` Mike Snitzer 2018-05-21 14:03 ` Mike Snitzer 2018-05-21 14:19 ` Jens Axboe [not found] ` <686d7df6-c7d1-48a6-b7ff-48dc8aff6a62-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> 2018-05-21 14:31 ` Mike Snitzer 2018-05-21 14:31 ` Mike Snitzer 2018-05-21 14:36 ` Jens Axboe [not found] ` <2bbeeb1a-8b99-b06a-eb9b-eb8523c16460-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> 2018-05-21 14:47 ` Mike Snitzer 2018-05-21 14:47 ` Mike Snitzer [not found] ` <20180521144703.GA19303-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2018-05-21 14:52 ` Jens Axboe 2018-05-21 14:52 ` Jens Axboe [not found] ` <4b343aef-e11c-73ba-1d88-7e73ca838cad-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> 2018-05-21 15:04 ` Mike Snitzer 2018-05-21 15:04 ` Mike Snitzer [not found] ` <20180521150439.GA19379-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2018-05-21 15:09 ` Jens Axboe 2018-05-21 15:09 ` Jens Axboe [not found] ` <61e30dcf-a01c-f47d-087a-12930caf9aef-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> 2018-05-21 15:18 ` Mike Snitzer 2018-05-21 15:18 ` Mike Snitzer [not found] ` <20180521151817.GA19454-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2018-05-21 15:36 ` Jens Axboe 2018-05-21 15:36 ` Jens Axboe [not found] ` <d01a150a-7752-f6ce-78f2-17a65c1e6fa5-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> 2018-05-21 16:09 ` Mike Snitzer 2018-05-21 16:09 ` Mike Snitzer [not found] ` <20180521160907.GA19553-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2018-05-21 16:20 ` Jens Axboe 2018-05-21 16:20 ` Jens Axboe [not found] ` <f9e3714c-b7c9-d5f6-4018-2a87dd5babb2-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> 2018-05-30 13:36 ` Mike Snitzer 2018-05-30 13:36 ` Mike Snitzer [not found] ` <20180530133629.GC5157-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2018-05-30 18:55 ` Jens Axboe 2018-05-30 18:55 ` Jens Axboe 2018-05-30 19:34 ` Kent Overstreet 2018-05-30 19:36 ` Jens Axboe 2018-05-30 19:36 ` Jens Axboe 2018-05-30 19:37 ` Mike Snitzer [not found] ` <20180530193707.GB6568-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2018-05-30 19:38 ` Jens Axboe 2018-05-30 19:38 ` Jens Axboe 2018-05-21 17:37 ` Kent Overstreet 2018-05-21 18:24 ` Mike Snitzer 2018-05-21 18:24 ` Mike Snitzer 2018-05-21 23:38 ` Kent Overstreet 2018-05-22 6:41 ` Christoph Hellwig [not found] ` <20180522064118.GA18704-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org> 2018-05-22 19:09 ` Mike Snitzer [this message] 2018-05-22 19:09 ` Mike Snitzer 2018-05-21 15:12 ` David Sterba 2018-05-21 15:18 ` Jens Axboe 2018-05-21 14:20 ` Jens Axboe 2018-05-30 22:24 ` Jens Axboe
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