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From: Davidlohr Bueso <dave@stgolabs.net>
To: Jan Kara <jack@suse.cz>
Cc: akpm@linux-foundation.org, mingo@kernel.org,
	peterz@infradead.org, torvalds@linux-foundation.org,
	kirill.shutemov@linux.intel.com, hch@infradead.org,
	ldufour@linux.vnet.ibm.com, mhocko@suse.com,
	mgorman@techsingularity.net, linux-kernel@vger.kernel.org,
	tytso@mit.edu, Davidlohr Bueso <dbueso@suse.de>
Subject: Re: [PATCH 15/17] fs/ext4: use cached rbtrees
Date: Wed, 19 Jul 2017 15:50:39 -0700
Message-ID: <20170719225039.GC14395@linux-80c1.suse> (raw)
In-Reply-To: <20170719074056.GA12546@quack2.suse.cz>

On Wed, 19 Jul 2017, Jan Kara wrote:

>Hum, so I'm somewhat undecided whether this is worth the churn. For free
>blocks rb_tree we use rb_first() only in ext4_mb_generate_from_freelist()
>which gets called only when generating new buddy bitmap from on-disk bitmap
>and we traverse the whole tree after that - thus the extra cost of
>rb_first() is a) well hidden in the total cost of iteration, b) rather rare
>anyway.

Yes, during some of the testing I did for this patch, I could not find trees
with more than just a handful of nodes, ie: while removing file(s). 

>
>Similarly for the H-tree directory code, we call rb_first() in
>ext4_dx_readdir() only to start an iteration over the whole B-tree and in
>such case I don't think optimizing rb_first() makes a big difference
>(maintaining cached value is going to have about the same cost as we save
>by using it).

Your reaction is rather expected, actually. Lets just leave this patch out.

Thanks,
Davidlohr

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-19  1:45 [PATCH -next v4 00/17] rbtree: cache leftmost node internally Davidlohr Bueso
2017-07-19  1:45 ` [PATCH 01/17] " Davidlohr Bueso
2017-07-19  1:45 ` [PATCH 02/17] rbtree: optimize root-check during rebalancing loop Davidlohr Bueso
2017-07-19  1:45 ` [PATCH 03/17] rbtree: add some additional comments for rebalancing cases Davidlohr Bueso
2017-07-19  1:45 ` [PATCH 04/17] lib/rbtree_test.c: make input module parameters Davidlohr Bueso
2017-07-19  1:45 ` [PATCH 05/17] lib/rbtree_test.c: add (inorder) traversal test Davidlohr Bueso
2017-07-19  1:45 ` [PATCH 06/17] lib/rbtree_test.c: support rb_root_cached Davidlohr Bueso
2017-07-19  1:45 ` [PATCH 07/17] sched/fair: replace cfs_rq->rb_leftmost Davidlohr Bueso
2017-07-19  1:45 ` [PATCH 08/17] sched/deadline: replace earliest dl and rq leftmost caching Davidlohr Bueso
2017-07-19  1:45 ` [PATCH 09/17] locking/rtmutex: replace top-waiter and pi_waiters " Davidlohr Bueso
2017-07-19  1:45 ` [PATCH 10/17] block/cfq: replace cfq_rb_root " Davidlohr Bueso
2017-07-19  7:46   ` Jan Kara
2017-07-19  1:45 ` [PATCH 11/17] lib/interval_tree: fast overlap detection Davidlohr Bueso
2017-07-22 17:52   ` Doug Ledford
2017-08-01 17:16   ` Michael S. Tsirkin
2017-07-19  1:45 ` [PATCH 12/17] lib/interval-tree: correct comment wrt generic flavor Davidlohr Bueso
2017-07-19  1:45 ` [PATCH 13/17] procfs: use faster rb_first_cached() Davidlohr Bueso
2017-07-19  1:46 ` [PATCH 14/17] fs/epoll: " Davidlohr Bueso
2017-07-19  1:46 ` [PATCH 15/17] fs/ext4: use cached rbtrees Davidlohr Bueso
2017-07-19  7:40   ` Jan Kara
2017-07-19 22:50     ` Davidlohr Bueso [this message]
2017-07-19  1:46 ` [PATCH 16/17] mem/memcg: cache rightmost node Davidlohr Bueso
2017-07-19  7:50   ` Michal Hocko
2017-07-26 21:09     ` Andrew Morton
2017-07-27  7:06       ` Michal Hocko
2017-07-19  1:46 ` [PATCH 17/17] block/cfq: cache rightmost rb_node Davidlohr Bueso
2017-07-19  7:59   ` Jan Kara

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