Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 15 Dec 2003 14:44:40 -0800 | From | John Salmon <> | Subject | question about max_readahead for ide devices in 2.4? |
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Several "tuning" recommendations suggest that sequential accesses of large files, and hence the performance of busy web servers, can be improved by changing the maximum readahead value with, e.g.,
echo 511 > /proc/sys/vm/max-readahead
But it looks to me like get_max_readahead in filemap.c ignores the value set by /proc/sys in favor of max_readahead[major][minor] whenever max_readahead[major] is non-NULL. And furthermore that max_readahead[major] IS initialized to non-NULL for ide devices in init_gendisk. (N.B. I'm looking at 2.4 sources).
Conclusion: echoing a value into /proc/sys/vm/max-readahead won't change the readahead behavior for already-probed IDE devices.
Is this correct, or am I missing something?
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