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Subject: Re: [RFC][patch] NAND partial page read functionality
From: Artem Bityutskiy <dedekind@infradead.org>
To: Alexey Korolev <akorolev@infradead.org>
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Date: Thu, 24 Apr 2008 13:45:53 +0300
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Hi,

On Thu, 2008-04-24 at 11:25 +0100, Alexey Korolev wrote:
> 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 perform=
ance 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?

> Also we investigated possibility to make more universal solution which in=
cludes both sub-page=20
> 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=20
> 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.

--=20
Best regards,
Artem Bityutskiy (=D0=91=D0=B8=D1=82=D1=8E=D1=86=D0=BA=D0=B8=D0=B9 =D0=90=
=D1=80=D1=82=D1=91=D0=BC)