On 02/23/2010 10:10 PM, Wu Fengguang wrote:
When lifting the default readahead size from 128KB to 512KB,
make sure it won't add memory pressure to small memory systems.
For read-ahead, the memory pressure is mainly readahead buffers consumed
by too many concurrent streams. The context readahead can adapt
readahead size to thrashing threshold well. So in principle we don't
need to adapt the default _max_ read-ahead size to memory pressure.
For read-around, the memory pressure is mainly read-around misses on
executables/libraries. Which could be reduced by scaling down
read-around size on fast "reclaim passes".
This patch presents a straightforward solution: to limit default
readahead size proportional to available system memory, ie.
512MB mem => 512KB readahead size
128MB mem => 128KB readahead size
32MB mem => 32KB readahead size (minimal)
Strictly speaking, only read-around size has to be limited. However we
don't bother to seperate read-around size from read-ahead size for now.
CC: Matt Mackall<mpm@xxxxxxxxxxx>
Signed-off-by: Wu Fengguang<fengguang.wu@xxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
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