From: NeilBrown <neilb@suse.com>
To: John Stoffel <john@stoffel.org>
Cc: Shaohua Li <shli@fb.com>,
linux-raid@vger.kernel.org, songliubraving@fb.com,
hch@infradead.org, dan.j.williams@intel.com, Kernel-team@fb.com
Subject: Re: [PATCH V4 00/13] MD: a caching layer for raid5/6
Date: Mon, 20 Jul 2015 10:03:45 +1000 [thread overview]
Message-ID: <20150720100345.63302007@noble> (raw)
In-Reply-To: <21927.51382.8600.700720@quad.stoffel.home>
On Thu, 16 Jul 2015 11:07:34 -0400 "John Stoffel" <john@stoffel.org>
wrote:
>
> So.... how will wrapping of sequence numbers be handled in the cache
> metadata on disk? They can't grow for ever...
Can't they?
A 64bit number incremented every millisecond can grow for half a
billion years. As far as I'm concerned, that is forever.
But even if we used 32bit numbers, it is very easy to handle looping
providing you have few than half of the numbers in use at any time.
So as long as we don't have more than 2 billion active transactions in
the log at once, there is no problem.
The kernel does some internal time keeping using "jiffies" which, on
32bit systems, cycle about every fortnight. A small amount of care is
enough that this doesn't cause problem.
NeilBrown
next prev parent reply other threads:[~2015-07-20 0:03 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-23 21:37 [PATCH V4 00/13] MD: a caching layer for raid5/6 Shaohua Li
2015-06-23 21:37 ` [PATCH V4 01/13] MD: add a new disk role to present cache device Shaohua Li
2015-06-23 21:37 ` [PATCH V4 02/13] raid5: directly use mddev->queue Shaohua Li
2015-06-23 21:37 ` [PATCH V4 03/13] raid5: cache log handling Shaohua Li
2015-06-23 21:37 ` [PATCH V4 04/13] raid5: cache part of raid5 cache Shaohua Li
2015-06-23 21:37 ` [PATCH V4 05/13] raid5: cache reclaim support Shaohua Li
2015-06-23 21:37 ` [PATCH V4 06/13] raid5: cache IO error handling Shaohua Li
2015-06-23 21:37 ` [PATCH V4 07/13] raid5: cache device quiesce support Shaohua Li
2015-06-23 21:37 ` [PATCH V4 08/13] raid5: cache recovery support Shaohua Li
2015-06-23 21:37 ` [PATCH V4 09/13] raid5: add some sysfs entries Shaohua Li
2015-06-23 21:38 ` [PATCH V4 10/13] raid5: don't allow resize/reshape with cache support Shaohua Li
2015-06-23 21:38 ` [PATCH V4 11/13] raid5: guarantee cache release stripes in correct way Shaohua Li
2015-06-23 21:38 ` [PATCH V4 12/13] raid5: enable cache for raid array with cache disk Shaohua Li
2015-06-23 21:38 ` [PATCH V4 13/13] raid5: skip resync if caching is enabled Shaohua Li
2015-07-02 3:25 ` [PATCH V4 00/13] MD: a caching layer for raid5/6 Yuanhan Liu
2015-07-02 17:11 ` Shaohua Li
2015-07-03 2:18 ` Yuanhan Liu
2015-07-08 1:56 ` NeilBrown
2015-07-08 5:44 ` Shaohua Li
2015-07-09 23:21 ` NeilBrown
2015-07-10 4:08 ` Shaohua Li
2015-07-10 4:36 ` NeilBrown
2015-07-10 4:52 ` Shaohua Li
2015-07-10 5:10 ` NeilBrown
2015-07-10 5:18 ` Shaohua Li
2015-07-10 6:42 ` NeilBrown
2015-07-10 17:48 ` Shaohua Li
2015-07-13 22:22 ` NeilBrown
2015-07-13 22:35 ` Shaohua Li
2015-07-15 0:45 ` Shaohua Li
2015-07-15 2:12 ` NeilBrown
2015-07-15 3:16 ` Shaohua Li
2015-07-15 4:06 ` NeilBrown
2015-07-15 19:49 ` Shaohua Li
2015-07-15 23:16 ` NeilBrown
2015-07-16 0:07 ` Shaohua Li
2015-07-16 1:22 ` NeilBrown
2015-07-16 4:13 ` Shaohua Li
2015-07-16 6:07 ` NeilBrown
2015-07-16 15:07 ` John Stoffel
2015-07-20 0:03 ` NeilBrown [this message]
2015-07-20 14:11 ` John Stoffel
2015-07-16 17:40 ` Shaohua Li
2015-07-17 3:47 ` NeilBrown
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