On Mon, Apr 12, 2010 at 12:43:00PM +0800, 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, I once read the ld code, it's more complex than I expected. > we could do a mmap of one page instead of the read. But that's more > expansive in general, isn't it? Right. Without considering IO, a simple read(512) is more efficient than mmap()+read+munmap(). Thanks, Fengguang -- 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>