[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CACVXFVNKQm_NYBX17YWndm4zbMbnV4K--o0SZXeT6LAUS5eU=A@mail.gmail.com>
Date: Fri, 15 Aug 2014 21:20:52 +0800
From: Ming Lei <ming.lei@...onical.com>
To: Zach Brown <zab@...bo.net>
Cc: Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Dave Kleikamp <dave.kleikamp@...cle.com>,
Benjamin LaHaise <bcrl@...ck.org>,
Christoph Hellwig <hch@...radead.org>,
Kent Overstreet <kmo@...erainc.com>, linux-aio@...ck.org,
linux-fsdevel@...r.kernel.org, Dave Chinner <david@...morbit.com>,
Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v1 1/9] aio: add aio_kernel_() interface
On 8/15/14, Zach Brown <zab@...bo.net> wrote:
> On Thu, Aug 14, 2014 at 11:50:32PM +0800, Ming Lei wrote:
>> From: Dave Kleikamp <dave.kleikamp@...cle.com>
>>
>> This adds an interface that lets kernel callers submit aio iocbs without
>> going through the user space syscalls. This lets kernel callers avoid
>> the management limits and overhead of the context. It will also let us
>> integrate aio operations with other kernel apis that the user space
>> interface doesn't have access to.
>>
>> This patch is based on Dave's posts in below links:
>>
>> https://lkml.org/lkml/2013/10/16/365
>> https://groups.google.com/forum/#!topic/linux.kernel/l7mogGJZoKQ
>
> (And some other werido's posts, almost 5 entire earth years ago:
> http://permalink.gmane.org/gmane.linux.file-systems/36246)
Wow, thank you guys for proposing the idea so early.
Care to add your Signed-off-by? And Dave
>
>> +struct kiocb *aio_kernel_alloc(gfp_t gfp, unsigned extra)
>> +{
>> + return kzalloc(sizeof(struct kiocb) + extra, gfp);
>
> Is kzalloc really necessary? It's insane, but in the past we've had
You are right, and kmalloc should be enough.
> people whine about the cycle costs of zeroing fields that are to be
> initialized:
>
> commit 23aee091d804efa8cc732a31c1ae5d625e1ec886
> Author: Jeff Moyer <jmoyer@...hat.com>
> Date: Tue Dec 15 16:47:49 2009 -0800
>
> dio: don't zero out the pages array inside struct dio
>
> Maybe add a guard value to the ctx and have submission freak out of it's
> called without being initialized? If callers really want to zero they
> can pass in __GFP_ZERO.
At least now, other fields won't be touched in kernel AIO path, and they
can be handled in future if need.
>
> The extra allocation at the end that's freed is nice, but the callers
> having a clumsy manual cast to access it isn't nice at all. Can you add
> a little helper to get a pointer to the extra allocation? That'd let
OK.
> the aio bits allocation the iocbs however the like (slab, per-cpu,
> whatever) and have extra allocations separate if that ends up making
> sense.
In the future, maybe it is needed for sake of performance, and now it is OK
to not introduce the extra complexity.
>
>> + iocb->ki_ctx = (void *)-1;
>
> The magic -1 is gross. Use a constant? (bonus points for having it use
> ERR_PTR() :))
OK.
>
>> + /*
>> + * use same policy with userspace aio, req may have been
>> + * completed already, so release it by aio completion.
>> + */
>> + if (ret != -EIOCBQUEUED)
>> + iocb->ki_obj.complete(iocb->ki_user_data, ret);
>
> I wonder if this needs to handle the restarting error codes like
> aio_complete() does.
For same reason, kernel path needn't restart too, and caller won't
see such error code.
>
> commit a0c42bac79731276c9b2f28d54f9e658fcf843a2
> Author: Jan Kara <jack@...e.cz>
> Date: Wed Sep 22 13:05:03 2010 -0700
>
> aio: do not return ERESTARTSYS as a result of AIO
>
> I like how this has evolved to get rid of the magic key and commands..
> just the ki_ctx and calling iter methods, nice stuff.
Thanks,
--
Ming Lei
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists