On 12/27/06, Linus Torvalds wrote: > - It never uses mprotect on the shared mappings, but it _does_ do: > "mincore()" - but the return values don't much matter (it's used > as a heuristic on which parts to hash, apparently) > > I double- and triple-checked this one, because I > did make changes to "mincore()", but those didn't go > into the affected kernels anyway (ie they are not in > plain 2.6.19, nor in 2.6.18.3 either) Correct, mincore is only used to check if it should delay the hash checking. > "madvise(MADV_WILLNEED)" > "msync(MS_ASYNC)" (or MS_SYNC if you use a command line flag) > "munmap()" of course > > - it never seems to mix mmap() and write() - it does _only_ mmap. > > - it seems to mmap/munmap the shared files in nice 64-page chunks, all > 64-page aligned in the file (ie it does NOT create one big mapping, it > has some kind of LRU of thse 64-page chunks). The only exception being > the last chunk, which it maps byte-accurate to the size. The length of the chunks is only page aligned on single file torrents, not so on multi-file torrents. I've attached a patch for rtorrent that will extend the length to the page boundary. > - I haven't checked whether it only ever has the same chunk mapped once > at a time. This should be the case, but two mapped chunks may share a page, sometimes with different r/w permissions. Jari Sundell