From: Randy Dunlap <rdunlap@infradead.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org, Gao Xiang <gaoxiang25@huawei.com>,
zhong jiang <zhongjiang@huawei.com>, Chao Yu <yuchao0@huawei.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: Tagged pointers in the XArray
Date: Tue, 28 Aug 2018 16:09:23 -0700 [thread overview]
Message-ID: <8352b2da-b638-2205-132b-f32893d1cdb7@infradead.org> (raw)
In-Reply-To: <20180828230329.GE11400@bombadil.infradead.org>
On 08/28/2018 04:03 PM, Matthew Wilcox wrote:
> On Tue, Aug 28, 2018 at 03:39:01PM -0700, Randy Dunlap wrote:
>> Just a question, please...
>>
>> On 08/28/2018 03:27 PM, Matthew Wilcox wrote:
>>>
>>> diff --git a/include/linux/xarray.h b/include/linux/xarray.h
>>> index c74556ea4258..d1b383f3063f 100644
>>> --- a/include/linux/xarray.h
>>> +++ b/include/linux/xarray.h
>>> @@ -150,6 +150,54 @@ static inline int xa_err(void *entry)
>>> return 0;
>>> }
>>>
>>> +/**
>>> + * xa_tag_pointer() - Create an XArray entry for a tagged pointer.
>>> + * @p: Plain pointer.
>>> + * @tag: Tag value (0, 1 or 3).
>>> + *
>>
>> What's wrong with a tag value of 2?
>
> That conflicts with the XArray's internal entries and you get a WARN_ON
> when you try to store it in the array.
>
>> and what happens when one is used? [I don't see anything preventing that.]
>
> Right, there's nothing preventing you from using the value 5 or 19
> or 16777216 either ... I did put in a WARN_ON_ONCE to begin with, but
> decided that was unnecessary.
>
> Right now our only user uses 0 and 1, so even documenting 3 as a
> possibility isn't _necessary_, but some day somebody is going to want
> to add FILE_NOT_FOUND
> https://thedailywtf.com/articles/What_Is_Truth_0x3f_
>
Thanks. :)
--
~Randy
next prev parent reply other threads:[~2018-08-28 23:09 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-28 22:27 Tagged pointers in the XArray Matthew Wilcox
2018-08-28 22:39 ` Randy Dunlap
2018-08-28 23:03 ` Matthew Wilcox
2018-08-28 23:09 ` Randy Dunlap [this message]
2018-08-28 23:24 ` Gao Xiang
2018-08-28 23:26 ` Gao Xiang
2018-08-29 16:17 ` Matthew Wilcox
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