On Mon, 3 Apr 2000, Alan Cox wrote:
>> Read-ahead (there is no write ahead) at mmap(2) is constrained
>> to ONE instance per entire process memory space.
>> That alone makes use of mmap(2) rather inefficient, doesn't it ?
>
>That seems odd. Quite a few programs open a file multiple times and mmap
>using different fd's to try and get multiple readaheads. I've never looked
>to see if that works on Linux too
In 2.2.x we always do unconditional readaround if the page fault generates
a page-cache miss. In 2.3.x the readaround can be optionally disabled
globally per-user-MM using madvise(MADV_RANDOM). The size of the
readaround is controlled by the sys/vm/page-cluster sysctl. As default the
readaround is large 64k (assuming page-size to be 4k).
Andrea
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