On Wed, Jan 22, 2014 at 09:21:40AM -0800, James Bottomley wrote: > On Wed, 2014-01-22 at 17:02 +0000, Chris Mason wrote: > > On Wed, 2014-01-22 at 15:19 +0000, Mel Gorman wrote: > > > On Wed, Jan 22, 2014 at 09:58:46AM -0500, Ric Wheeler wrote: > > > > On 01/22/2014 09:34 AM, Mel Gorman wrote: > > > > >On Wed, Jan 22, 2014 at 09:10:48AM -0500, Ric Wheeler wrote: > > > > >>On 01/22/2014 04:34 AM, Mel Gorman wrote: > > > > >>>On Tue, Jan 21, 2014 at 10:04:29PM -0500, Ric Wheeler wrote: > > > > >>>>One topic that has been lurking forever at the edges is the current > > > > >>>>4k limitation for file system block sizes. Some devices in > > > > >>>>production today and others coming soon have larger sectors and it > > > > >>>>would be interesting to see if it is time to poke at this topic > > > > >>>>again. > > > > >>>> > > > > >>>Large block support was proposed years ago by Christoph Lameter > > > > >>>(http://lwn.net/Articles/232757/). I think I was just getting started > > > > >>>in the community at the time so I do not recall any of the details. I do > > > > >>>believe it motivated an alternative by Nick Piggin called fsblock though > > > > >>>(http://lwn.net/Articles/321390/). At the very least it would be nice to > > > > >>>know why neither were never merged for those of us that were not around > > > > >>>at the time and who may not have the chance to dive through mailing list > > > > >>>archives between now and March. > > > > >>> > > > > >>>FWIW, I would expect that a show-stopper for any proposal is requiring > > > > >>>high-order allocations to succeed for the system to behave correctly. > > > > >>> > > > > >>I have a somewhat hazy memory of Andrew warning us that touching > > > > >>this code takes us into dark and scary places. > > > > >> > > > > >That is a light summary. As Andrew tends to reject patches with poor > > > > >documentation in case we forget the details in 6 months, I'm going to guess > > > > >that he does not remember the details of a discussion from 7ish years ago. > > > > >This is where Andrew swoops in with a dazzling display of his eidetic > > > > >memory just to prove me wrong. > > > > > > > > > >Ric, are there any storage vendor that is pushing for this right now? > > > > >Is someone working on this right now or planning to? If they are, have they > > > > >looked into the history of fsblock (Nick) and large block support (Christoph) > > > > >to see if they are candidates for forward porting or reimplementation? > > > > >I ask because without that person there is a risk that the discussion > > > > >will go as follows > > > > > > > > > >Topic leader: Does anyone have an objection to supporting larger block > > > > > sizes than the page size? > > > > >Room: Send patches and we'll talk. > > > > > > > > > > > > > I will have to see if I can get a storage vendor to make a public > > > > statement, but there are vendors hoping to see this land in Linux in > > > > the next few years. > > > > > > What about the second and third questions -- is someone working on this > > > right now or planning to? Have they looked into the history of fsblock > > > (Nick) and large block support (Christoph) to see if they are candidates > > > for forward porting or reimplementation? > > > > I really think that if we want to make progress on this one, we need > > code and someone that owns it. Nick's work was impressive, but it was > > mostly there for getting rid of buffer heads. If we have a device that > > needs it and someone working to enable that device, we'll go forward > > much faster. > > Do we even need to do that (eliminate buffer heads)? No, the reason bufferheads were replaced was that a bufferhead can only reference a single page. i.e. the structure is that a page can reference multipl bufferheads (block size >= page size) but a bufferhead can't refernce multiple pages which is what is needed for block size > page size. fsblock was designed to handle both cases. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
