* Jesper Juhl (jj@xxxxxxxxxxxxx) wrote: > Do you rely only on the checksum or do you actually compare pages to check > they are 100% identical before sharing? Checksum has absolutely nothing to do w/ finding if two pages match. It's only used as a heuristic to suggest whether a single page has changed. If that page is changing we won't bother trying to find a match for it. Here's an example of the life of a page w.r.t checksum. 1. checksum = uninitialized 2. first time page is found, checksum it (checksum = A). if checksum has changed (uninitialize != A) don't go any further w/ that page 3. next time page is found, checksum it (checksum = B). if checksum has change (A != B) don't go any further w/ that page 4. next time page is found, checksum it (checksum = B). if checksum has changed (B == B)...it hasn't, continue processing the page later if a match is found in the tree (which is sorted by _contents_, i.e. memcmp) we'll attempt to merge the pages which at it's very core does: if (pages_identical(oldpage, newpage)) ret = replace_page(vma, oldpage, newpage, orig_pte, newprot); pages_identical? you guessed it...just does: r = memcmp(addr1, addr2, PAGE_SIZE) thanks, -chris -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
