On Fri, Aug 01, 2014 at 05:24:59PM +0200, Jan Kara wrote: > OK, makes sense. But then if there's heavy IO going on, anything that has > IO pending on it is pinned and IO completion can easily take something > close to a second or more. So meeting subsecond deadlines may be tough even > for ordinary data pages under heavy load, even more so for metadata where > there are further constraints. OTOH phones aren't usually IO bound so in > practice it needn't be so bad ;). Yeah, typically phones are not IO bound :-) > So if it is sub-second unless someone > loads the storage, then that sounds doable even for metadata. But we'll > need to attach ->migratepage callback to blkdev pages and at least in ext4 > case teach it how to move pages tracked by the journal. Right, making it possible at all if of course much prefered over not possible, regardless of timeliness :-) > > Sadly its not only mobile devices that excel in crappy hardware, there's > > plenty desktop stuff that could use this too, like some of the v4l > > devices iirc. > Yeah, but in such usecases the guarantees we can offer for completion of > migration are even more vague :(. Yeah, lets start by making it possible, after that we can maybe look at making it better, who knows.
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