[RFC][patch] NAND partial page read functionality

[Alexey Korolev]

Hi,

> > Oh I'm glad to hear that this patch is needful. In fact I did
> > not drop it. We did some more investigations about integration subpage
> >  read in background. We tried to remove some drawback caused by
> > invalidation of prestored page in do_read_ops function. (We have found
> > that on large read requests nand subpage read causes ~10% of read performance degradation. I
> > wanted to remove but changes made code ugly and saved only 5%)
> 
> Err, are you referring this chip->pagebuf cache? Have you considered
> making it more complex and keep track of individual sub-pages within the
> pagebuf? You say it introduces a lot of ugliness? May be you could
> somehow separate this ugliness out nicely somehow?
Yes. I mean chip->pagebuf cache. From point of performacne the best
would be traking sub_pages within the pagebuf. But it is too complex and
brings ugliness. Sure I will definetely separate it.

> 
> > Also we investigated possibility to make more universal solution which includes both sub-page 
> > read and partial page write. As it was discussed in December. In fact the partial page write did not
> > give any benefits at all as file system operates write_size. If we reduce writesize JFFS2 will write data by 
> > small chunks only and it will cause strong performance degradation. (it
> > brings more cons than pros until serious hacks in JFFS2 will be
> > implemented)
> 
> Well, in any case, if you have something for writes, this should be a
> separate story.
> 
>