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SubjectRe: elevator algorithm bug in ll_rw_blk.c

On Sun, 15 Nov 1998 20:38:05 +0100 (MET), Gerard Roudier
<> said:

> My understanding of Linux architecture is that IO blocks coalescing only
> occurs in ll_rw_blk.c.

Yes, except for scsi which does its Own Thing, of course.

> If it fails the coalescing then Linux will just do 1 IO for each
> block. When you have lots of memory, it may happen the number of
> entries in the request array (NR_REQUEST) be not enough for this
> coalescing to occur in some situations that may not be rare given the
> way the buffer cache actually work.

The way it actually works, sequential writes tend to be kept in
sequential order in the buffer cache lists, so the typical cases work
pretty well. All the benchmarks show that sequential filesystem writes
work very well.


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