Re: Advice sought on how to lock multiple pages in ->prepare_write and ->writepage

[Bryan Henderson <hbryan@xxxxxxxxxx>]

>OOC, have you folks measured any performance improvements at all
>using larger IOs (doing multi-page bios?) with larger blocksizes?

First, let me clarify that by "larger I/O" you mean a larger unit of I/O 
submitted to the block layer (doing multi-page bios), because people often 
say "larger I/O" to mean larger units of I/O from Linux to the device, and 
the two are only barely coupled.

Blocksize > page size doesn't mean multi-page bios as long as VM is still 
managing the file cache.  VM pages in and out one page at a time.

To get multi-page bios (in any natural way), you need to throw out not 
only the generic file read/write routines, but the page cache as well.

Every time I've looked at multi-page bios, I've been unable to see any 
reason that they would be faster than multiple single-page bios.  But I 
haven't seen any experiments.

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Bryan Henderson                     IBM Almaden Research Center
San Jose CA                         Filesystems