From: Sasha Levin <levinsasha928@gmail.com>
To: Josh Triplett <josh@joshtriplett.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Pedro Alves <palves@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>, Tejun Heo <tj@kernel.org>,
torvalds@linux-foundation.org, akpm@linux-foundation.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
paul.gortmaker@windriver.com, davem@davemloft.net, mingo@elte.hu,
ebiederm@xmission.com, aarcange@redhat.com, ericvh@gmail.com,
netdev@vger.kernel.org, eric.dumazet@gmail.com, axboe@kernel.dk,
agk@redhat.com, dm-devel@redhat.com, neilb@suse.de,
ccaulfie@redhat.com, teigland@redhat.com,
Trond.Myklebust@netapp.com, bfields@fieldses.org,
fweisbec@gmail.com, jesse@nicira.com,
venkat.x.venkatsubra@oracle.com, ejt@redhat.com,
snitzer@redhat.com, edumazet@google.com,
linux-nfs@vger.kernel.org, dev@openvswitch.org,
rds-devel@oss.oracle.com, lw@cn.fujitsu.com
Subject: Re: [PATCH v3 01/17] hashtable: introduce a small and naive hashtable
Date: Thu, 06 Sep 2012 17:49:41 +0200 [thread overview]
Message-ID: <5048C615.4070204@gmail.com> (raw)
In-Reply-To: <20120906145545.GA17332@leaf>
On 09/06/2012 04:55 PM, Josh Triplett wrote:
> On Thu, Sep 06, 2012 at 03:53:58PM +0200, Sasha Levin wrote:
>> On 09/04/2012 07:01 PM, Mathieu Desnoyers wrote:
>>>> #define do_for_each_ftrace_rec(pg, rec) \
>>>>> for (pg = ftrace_pages_start, rec = &pg->records[pg->index]; \
>>>>> pg && rec == &pg->records[pg->index]; \
>>>>> pg = pg->next) \
>>>>> for (rec = pg->records; rec < &pg->records[pg->index]; rec++)
>>> Maybe in some cases there might be ways to combine the two loops into
>>> one ? I'm not seeing exactly how to do it for this one, but it should
>>> not be impossible. If the inner loop condition can be moved to the outer
>>> loop, and if we use (blah ? loop1_conf : loop2_cond) to test for
>>> different conditions depending on the context, and do the same for the
>>> 3rd argument of the for() loop. The details elude me for now though, so
>>> maybe it's complete non-sense ;)
>>>
>>> It might not be that useful for do_for_each_ftrace_rec, but if we can do
>>> it for the hash table iterator, it might be worth it.
>>
>> So I think that for the hash iterator it might actually be simpler.
>>
>> My solution to making 'break' work in the iterator is:A code like that doesn
>>
>> for (bkt = 0, node = NULL; bkt < HASH_SIZE(name) && node == NULL; bkt++)
>> hlist_for_each_entry(obj, node, &name[bkt], member)
>>
>> We initialize our node loop cursor with NULL in the external loop, and the
>> external loop will have a new condition to loop while that cursor is NULL.
>>
>> My logic is that we can only 'break' when we are iterating over an object in the
>> internal loop. If we're iterating over an object in that loop then 'node != NULL'.
>>
>> This way, if we broke from within the internal loop, the external loop will see
>> node as not NULL, and so it will stop looping itself. On the other hand, if the
>> internal loop has actually ended, then node will be NULL, and the outer loop
>> will keep running.
>>
>> Is there anything I've missed?
>
> Looks reasonable. However, it would break (or rather, not break) on
> code like this:
>
> hash_for_each_entry(...) {
> if (...) {
> foo(node);
> node = NULL;
> break;
> }
> }
>
> Hiding the double loop still seems error-prone.
I think that that code doesn't make sense. The users of hlist_for_each_* aren't
supposed to be changing the loop cursor.
We have three options here:
1. Stuff everything into a single for(). While not too difficult, it will make
the readability of the code difficult as it will force us to abandon using
hlist_for_each_* macros.
2. Over-complicate everything, and check for 'node == NULL && obj &&
obj->member.next == NULL' instead. That one will fail only if the user has
specifically set the object as the last object in the list and the node as NULL.
3. Use 2 loops which might not work properly if the user does something odd,
with a big fat warning above them.
To sum it up, I'd rather go with 3 and let anyone who does things he shouldn't
be doing break.
Thanks,
Sasha
next prev parent reply other threads:[~2012-09-06 15:49 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-22 2:26 [PATCH v3 00/17] generic hashtable implementation Sasha Levin
2012-08-22 2:26 ` [PATCH v3 01/17] hashtable: introduce a small and naive hashtable Sasha Levin
2012-08-22 18:01 ` Tejun Heo
2012-08-22 23:54 ` Ryan Mallon
2012-08-23 0:24 ` Sasha Levin
2012-08-23 20:04 ` Tejun Heo
2012-08-24 19:47 ` Sasha Levin
2012-08-24 19:59 ` Tejun Heo
2012-08-24 20:11 ` Sasha Levin
2012-08-24 20:33 ` Tejun Heo
2012-08-24 20:53 ` Sasha Levin
2012-08-24 21:23 ` Tejun Heo
2012-08-24 22:59 ` Sasha Levin
2012-08-24 23:07 ` Tejun Heo
2012-08-25 4:24 ` Mathieu Desnoyers
2012-08-28 9:56 ` Sasha Levin
2012-08-28 10:11 ` Mathieu Desnoyers
2012-08-28 11:27 ` Sasha Levin
2012-08-28 11:56 ` Mathieu Desnoyers
2012-08-28 23:00 ` Mathieu Desnoyers
2012-09-04 15:35 ` Steven Rostedt
2012-09-04 16:30 ` Pedro Alves
2012-09-04 16:40 ` Pedro Alves
2012-09-04 17:01 ` Mathieu Desnoyers
2012-09-06 13:53 ` Sasha Levin
2012-09-06 14:19 ` Pedro Alves
2012-09-06 14:33 ` Mathieu Desnoyers
2012-09-06 14:36 ` David Laight
2012-09-06 14:55 ` Josh Triplett
2012-09-06 15:11 ` Steven Rostedt
2012-09-06 15:49 ` Sasha Levin [this message]
2012-09-06 16:00 ` Steven Rostedt
2012-09-06 16:21 ` Sasha Levin
2012-09-06 16:50 ` Mathieu Desnoyers
2012-09-06 17:01 ` Sasha Levin
2012-09-06 17:02 ` Mathieu Desnoyers
2012-09-06 17:15 ` Steven Rostedt
2012-09-04 17:17 ` Steven Rostedt
2012-09-04 17:21 ` Pedro Alves
2012-09-04 20:59 ` Steven Rostedt
2012-09-04 21:51 ` Pedro Alves
2012-09-04 22:41 ` Steven Rostedt
2012-09-04 22:58 ` Pedro Alves
2012-09-04 23:27 ` Steven Rostedt
2012-09-04 16:32 ` Mathieu Desnoyers
2012-08-22 2:26 ` [PATCH v3 02/17] userns: use new hashtable implementation Sasha Levin
2012-08-22 2:26 ` [PATCH v3 03/17] mm,ksm: " Sasha Levin
2012-08-22 2:26 ` [PATCH v3 04/17] workqueue: " Sasha Levin
2012-08-22 18:05 ` Tejun Heo
2012-08-22 2:27 ` [PATCH v3 05/17] mm/huge_memory: " Sasha Levin
2012-08-22 2:27 ` [PATCH v3 06/17] tracepoint: " Sasha Levin
2012-08-22 2:27 ` [PATCH v3 07/17] net,9p: " Sasha Levin
2012-08-22 2:27 ` [PATCH v3 08/17] block,elevator: " Sasha Levin
2012-08-22 2:27 ` [PATCH v3 09/17] SUNRPC/cache: " Sasha Levin
2012-08-22 2:27 ` [PATCH v3 10/17] dlm: " Sasha Levin
2012-08-22 2:27 ` [PATCH v3 11/17] net,l2tp: " Sasha Levin
2012-08-22 2:27 ` [PATCH v3 12/17] dm: " Sasha Levin
2012-08-22 2:27 ` [PATCH v3 13/17] lockd: " Sasha Levin
2012-08-22 11:47 ` J. Bruce Fields
2012-08-22 12:13 ` Sasha Levin
2012-08-22 13:12 ` J. Bruce Fields
2012-08-22 13:22 ` Mathieu Desnoyers
2012-08-22 17:32 ` Sasha Levin
2012-08-22 2:27 ` [PATCH v3 14/17] net,rds: " Sasha Levin
2012-08-22 2:27 ` [PATCH v3 15/17] openvswitch: " Sasha Levin
2012-08-22 2:27 ` [PATCH v3 16/17] tracing output: " Sasha Levin
2012-08-22 2:27 ` [PATCH v3 17/17] SUNRPC: use new hashtable implementation in auth Sasha Levin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5048C615.4070204@gmail.com \
--to=levinsasha928@gmail.com \
--cc=Trond.Myklebust@netapp.com \
--cc=aarcange@redhat.com \
--cc=agk@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=axboe@kernel.dk \
--cc=bfields@fieldses.org \
--cc=ccaulfie@redhat.com \
--cc=davem@davemloft.net \
--cc=dev@openvswitch.org \
--cc=dm-devel@redhat.com \
--cc=ebiederm@xmission.com \
--cc=edumazet@google.com \
--cc=ejt@redhat.com \
--cc=eric.dumazet@gmail.com \
--cc=ericvh@gmail.com \
--cc=fweisbec@gmail.com \
--cc=jesse@nicira.com \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-nfs@vger.kernel.org \
--cc=lw@cn.fujitsu.com \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@elte.hu \
--cc=neilb@suse.de \
--cc=netdev@vger.kernel.org \
--cc=palves@redhat.com \
--cc=paul.gortmaker@windriver.com \
--cc=rds-devel@oss.oracle.com \
--cc=rostedt@goodmis.org \
--cc=snitzer@redhat.com \
--cc=teigland@redhat.com \
--cc=tj@kernel.org \
--cc=torvalds@linux-foundation.org \
--cc=venkat.x.venkatsubra@oracle.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).