On 11/21/19 5:49 AM, Jackie Liu wrote: > > > On 2019/11/21 20:40, Pavel Begunkov wrote: >>> 在 2019/11/21 17:43, Pavel Begunkov 写道: >>>> On 11/21/2019 12:26 PM, Jackie Liu wrote: >>>>> 2019年11月21日 16:54，Pavel Begunkov <asml.silence@xxxxxxxxx> 写道： >>>>>> >>>>>> If there is a DRAIN in the middle of a link, it uses shadow req. Defer >>>>>> the next request/link instead. This: >>>>>> >>>>>> Pros: >>>>>> 1. removes semi-duplicated code >>>>>> 2. doesn't allocate memory for shadows >>>>>> 3. works better if only the head marked for drain >>>>> >>>>> I thought about this before, just only drain the head, but if the >>>>> latter IO depends >>>>> on the link-list, then latter IO will run in front of the link-list. >>>>> If we think it >>>>> is acceptable, then I think it is ok for me. >>>> >>>> If I got your point right, latter requests won't run ahead of the >>>> link-list. There shouldn't be change of behaviour. >>>> >>>> The purpose of shadow requests is to mark some request right ahead of >>>> the link for draining. This patch uses not a specially added shadow >>>> request, but the following regular one. And, as drained IO shouldn't be >>>> issued until every request behind completed, this should give the same >>>> effect. >>>> >>>> Am I missed something? >>> >>> Thanks for explaining. This is also correct, if I understand >>> correctly, It seems that other IOs will wait for all the links are >>> done. this is a little different, is it? >> >> Yes, you're right, it also was briefly stated in the patch description >> (see Cons). I hope, links + drain in the middle is an uncommon case. >> But it can be added back, but may become a little bit uglier. >> >> What do you think, should we care about this case? > > Yes, this is a very tiny scene. When I first time wrote this part of the > code, my suggestion was to ban it directly. > > For this patch, I am fine, Jens, what do you think. I am fine with it as well, it'd be nice to get rid of needing that extra request. Was that a reviewed-by from you? It'd be nice to get these more formally so I can add the attributes. I'll drop the other patch. > The mailing list always rejects my mail, is my smtp server IP banned? Probably because you have text/html in your email, the list is pretty picky when it comes to anything that isn't just text/plain. -- Jens Axboe
