From: Waiman Long <longman@redhat.com>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Jan Kara <jack@suse.com>, Jeff Layton <jlayton@poochiereds.net>,
"J. Bruce Fields" <bfields@fieldses.org>,
Tejun Heo <tj@kernel.org>,
Christoph Lameter <cl@linux-foundation.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Andi Kleen <andi@firstfloor.org>,
Dave Chinner <dchinner@redhat.com>,
Boqun Feng <boqun.feng@gmail.com>
Subject: Re: [PATCH v7 5/6] lib/dlock-list: Enable faster lookup with hashing
Date: Mon, 9 Oct 2017 10:16:21 -0400 [thread overview]
Message-ID: <95cbbab7-246d-fd42-23e3-19aa5bd8efe5@redhat.com> (raw)
In-Reply-To: <20171009130827.GC5131@linux-80c1.suse>
On 10/09/2017 09:08 AM, Davidlohr Bueso wrote:
> On Thu, 05 Oct 2017, Waiman Long wrote:
>
>> Insertion and deletion is relatively cheap and mostly contention
>> free for dlock-list. Lookup, on the other hand, can be rather costly
>> because all the lists in a dlock-list will have to be iterated.
>>
>> Currently dlock-list insertion is based on the cpu that the task is
>> running on. So a given object can be inserted into any one of the
>> lists depending on what the current cpu is.
>>
>> This patch provides an alternative way of list selection. The caller
>> can provide a object context which will be hashed to one of the list
>> in a dlock-list. The object can then be added into that particular
>> list. Lookup can be done by iterating elements in the provided list
>> only instead of all the lists in a dlock-list.
>
> Unless I'm misusing the api, I could not find a standard way of
> iterating a _particular_ list head (the one the dlock_list_hash()
> returned). This is because iterators always want the all the heads.
>
> Also, in my particular epoll case I'd need the head->lock _not_ to
> be dropped after the iteration, and therefore is pretty adhoc.
> Currently we do:
>
> dlist_for_each_entry() {
> // acquire head->lock for each list
> }
> // no locks held
> dlist_add()
>
> I'm thinking perhaps we could have dlist_check_add() which passes a
> callback to ensure we want to add the node. The function could acquire
> the head->lock and not release it until the very end.
With the dlock_list_hash(), dlock-list is degenerated into a pool of
list where one is chosen by hashing. So the regular list iteration
macros like list_for_each_entry() can then be used. Of course, you have
to explicitly do the lock and unlock operation.
I could also encapsulate it a bit with inlined function like
dlock_list_single_iter_init(iter, dlist, head, flags)
It could set up the iterator properly to iterate only 1 list. The flags
can be to indicate holding the lock after iteration. In this case,
dlock_list_unlock(iter) will have to be called to do the unlock. I could
add a patch to do that if you prefer that route.
Cheers,
Longman
next prev parent reply other threads:[~2017-10-09 14:16 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-05 18:43 [PATCH v7 0/6] vfs: Use dlock list for SB's s_inodes list Waiman Long
2017-10-05 18:43 ` [PATCH v7 1/6] lib/dlock-list: Distributed and lock-protected lists Waiman Long
2017-10-10 5:35 ` Boqun Feng
2017-10-13 21:10 ` Waiman Long
2017-10-18 8:55 ` Boqun Feng
2017-10-05 18:43 ` [PATCH v7 2/6] vfs: Remove unnecessary list_for_each_entry_safe() variants Waiman Long
2017-10-05 18:43 ` [PATCH v7 3/6] vfs: Use dlock list for superblock's inode list Waiman Long
2017-10-05 18:43 ` [PATCH v7 4/6] lib/dlock-list: Make sibling CPUs share the same linked list Waiman Long
2017-10-09 15:40 ` Jan Kara
2017-10-09 16:14 ` Waiman Long
2017-10-05 18:43 ` [PATCH v7 5/6] lib/dlock-list: Enable faster lookup with hashing Waiman Long
2017-10-09 13:08 ` Davidlohr Bueso
2017-10-09 14:16 ` Waiman Long [this message]
2017-10-09 16:03 ` Davidlohr Bueso
2017-10-09 16:11 ` Waiman Long
2017-10-05 18:43 ` [PATCH v7 6/6] lib/dlock-list: Add an IRQ-safe mode to be used in interrupt handler Waiman Long
2017-10-13 15:45 ` [PATCH v7 7/6] fs/epoll: scale nested callbacks Davidlohr Bueso
2017-10-16 19:30 ` Jason Baron
2017-10-17 15:53 ` Davidlohr Bueso
2017-10-18 14:06 ` Jason Baron
2017-10-18 15:44 ` Davidlohr Bueso
2017-10-17 19:36 ` [PATCH v7 8/9] lib/dlock-list: Export symbols and add warnings Waiman Long
2017-10-17 19:36 ` [PATCH v7 9/9] lib/dlock-list: Unique lock class key for each allocation call site Waiman Long
2017-10-26 18:28 ` [PATCH v7 0/6] vfs: Use dlock list for SB's s_inodes list Waiman Long
2017-10-27 0:58 ` Boqun Feng
2017-10-27 20:19 ` Waiman Long
2017-10-27 20:10 ` [PATCH v7 10/10] lib/dlock-list: Fix use-after-unlock problem in dlist_for_each_entry_safe() Waiman Long
2017-10-30 9:06 ` Jan Kara
2017-10-30 14:06 ` Boqun Feng
2017-10-30 14:11 ` Davidlohr Bueso
2017-10-30 14:15 ` Waiman Long
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