Re: [PATCH 00/32] Adaptive readahead V14

[Wu Fengguang <wfg@mail.ustc.edu.cn>]

On Sat, May 27, 2006 at 09:29:46PM +0400, Michael Tokarev wrote:
> How the new readahead logic works with media read errors?
> Current linux behavior is questionable (it killed my dvd drive
> for example, due to too many retries to read a single bad block
> on a CD-Rom), it - I think - should be to stop reading ahead if
> an read error occurs, instead of re-trying, and only retry to
> read that block (if at all) when and only when an application
> asks for that block.  I'm unsure when it should "resume reading
> ahead" again (ie, like, setting ra to 0 on first error, and
> restoring it back if we trying to read past the bad block.. or
> set it to 0, and try to increase it on subsequent reads one by
> one back to the original value, or...) - but that's probably
> different story, for now, i think just setting ra to 0 on read
> error will be sufficient...

It's not quite reasonable for readahead to worry about media errors.
If the media fails, fix it. Or it will hurt read sooner or later.