Re: [PATCH 2/4] page_cache_readahead: remove duplicated code

[Steven Pratt <slpratt@austin.ibm.com>]

Ram wrote:

>On Tue, 2005-01-25 at 03:59, Oleg Nesterov wrote:
>  
>
>>Cases "no ahead window" and "crossed into ahead window"
>>can be unified.
>>    
>>
>
>
>No. There is a reason why we had some duplication. With your patch,
>we will end up reading-on-demand instead of reading ahead.
>
>When we notice a sequential reads have resumed, we first read in the
>data that is requested. 
>However if the read request is for more pages than what are being held
>in the current window, we make the ahead window as the current window
>and read in more pages in the ahead window. Doing that gives the
>opportunity of always having pages in the ahead window when the next
>sequential read request comes in.  If we apply this patch, we will
>always have to read the pages that are being requested instead of
>satisfying them from the ahead window.
>  
>
Ah, you are right! 

>Ok, if this does not make it clear, here is another way of proving that
>your patch does not exactly behave the way it did earlier.
>
>With your patch you will have only one call to
>block_page_cache_readahead(), when earlier there could be cases where
>block_page_cache_readahead() could be called twice.
>
>Am I am making sense?
>

Completely, this patch should not be applied.  Good catch.

Steve

>RP
> 
>  
>