On 04/11/2010 09:43 PM, drepper@xxxxxxxxx wrote:
On Sun, Apr 11, 2010 at 19:27, Wu Fengguang <fengguang.wu@xxxxxxxxx>
wrote:
Yes, every binary/library starts with this 512b read. It is requested
by ld.so/ld-linux.so, and will trigger a 4-page readahead. This is not
good readahead. I wonder if ld.so can switch to mmap read for the
first read, in order to trigger a larger 128kb readahead.
We first need to know the sizes of the segments and their location in
the binary. The binaries we use now are somewhat well laid out. The
read-only segment starts at offset 0 etc. But this doesn't have to be
the case. The dynamic linker has to be generic. Also, even if we
start mapping at offset zero, now much to map? The file might contain
debug info which must not be mapped. Therefore the first read loads
enough of the headers to make all of the decisions. Yes, we could do
a mmap of one page instead of the read. But that's more expansive in
general, isn't it?
Can this not be cached for prelinked files? I think it is reasonable to
optimize the gnu dynamic linker to optimize for an optimal layout
produced by gnu tools of the same generation.
Taras
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxxx For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>