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SubjectRe: [RFC DRAFT PATCH] per-buffered-write stream IDs
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On Tue, Apr 21, 2015 at 10:12 AM, Jens Axboe <axboe@fb.com> wrote:
> On 04/21/2015 11:09 AM, Ming Lin wrote:
>>
>> Hi Jens,
>>
>> This RFC DRAFT patch is on top of your "[PATCH v2] Support for write
>> stream IDs"
>> I throw it out early to get comments if it's the way to go.
>>
>> Quote LWN(http://lwn.net/Articles/638722):
>>
>> "There would be clear value in a closer association between stream IDs
>> and specific buffered-write operations. Getting there would require
>> storing
>> the stream ID with each dirtied page, though; that, in turn, almost
>> certainly
>> implies shoehorning the stream ID into the associated page structure.
>> That would not be an easy task; it is not surprising that it is not a part
>> of
>> this patch set. Should the lack of per-buffered-write stream IDs prove to
>> be
>> a serious constraint in the future, somebody will certainly be motivated
>> to
>> try to find a place to store another eight bits in struct page."
>>
>> This draft patch stores stream_id in buffer head instead of page.
>
>
> This is pointless. You need to store it in the page, if the whole point is
> that you want this to be trackable. And adding it to struct page would be a
> no-go, we can't increase the size of that. See various other discussions
> around, for instance, IO priorities for buffered writeback and tracking that
> state on the side.

I googled, but didn't find related discussions.
Could you please point me a link?

Thanks.


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