Re: [PATCH 1/4] scatterlist: new helper functions
From: Andrew Morton
Date: Wed Mar 16 2011 - 18:34:25 EST
On Tue, 15 Mar 2011 21:18:14 -0700 (PDT)
Alex Dubov <oakad@xxxxxxxxx> wrote:
> > I don't think so.
> > Splitting (or merging) a request and playing with sg lists
> > inside a
> > driver is a bad idea. Such should be done in the block
> > layer.
> > I still don't see why the block layer can't do that for the
> > driver.
> > I believe that the helper functions for such should not be
> > added.
> In a particular case of flash-like devices, letting the block layer
> split requests into memory sequential blocks too often results in
> unnecessary fragmentation of writes/erases.
> If only one sg entry is requested from the block layer, it will be (more
> often than not) only 1 or 2 pages in length, even if total size of
> prospective write request spans multiple erase blocks.
> So there are really only two options for legacy memorystick driver:
> 1. Play with scatterlists explicitly.
> 2. Make it an MTD backend, rather then stand-alone block device.
> The second option makes more sense, but it is not necessarily the optimal
> approach for implementation of this particular media format.
Do you believe that any other driver is likely to ue the sg
infrastructure which this patch adds? Should those additions be
internal to the memstick code, at least for now?
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