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SubjectRe: [patch 5/9] Guest page hinting: mlocked pages.
Martin Schwidefsky wrote:
> diff -urpN linux-2.6/mm/memory.c linux-2.6-patched/mm/memory.c
> --- linux-2.6/mm/memory.c 2006-09-01 12:50:24.000000000 +0200
> +++ linux-2.6-patched/mm/memory.c 2006-09-01 12:50:24.000000000 +0200
> @@ -2523,6 +2523,31 @@ int make_pages_present(unsigned long add
> BUG_ON(addr >= end);
> BUG_ON(end > vma->vm_end);
> len = (end+PAGE_SIZE-1)/PAGE_SIZE-addr/PAGE_SIZE;
> +
> + if (page_host_discards() && (vma->vm_flags & VM_LOCKED)) {
> + int rlen = len;
> + ret = 0;
> + while (rlen > 0) {
> + struct page *page_refs[32];
> + int chunk, cret, i;
> +
> + chunk = rlen < 32 ? rlen : 32;
> + cret = get_user_pages(current, current->mm, addr,
> + chunk, write, 0,
> + page_refs, NULL);
> + if (cret > 0) {
> + for (i = 0; i < cret; i++)
> + page_cache_release(page_refs[i]);
> + ret += cret;
> + }
> + if (cret < chunk)
> + return ret ? : cret;
> + addr += 32*PAGE_SIZE;
> + rlen -= 32;
> + }
> + return ret == len ? 0 : -1;
> + }
> +
> ret = get_user_pages(current, current->mm, addr,
> len, write, 0, NULL, NULL);
> if (ret < 0)
>

This seems like a bit of unneeded complexity. Since you've already
changed get_user_pages, why not add a follow flag to release the page
cache, and simply pass it to get_user_pages, instead of trying to fetch
the page list back. In particular, write and force arguments to
get_user_pages look very ripe for combining into a flags field. Sure,
get_user_pages now has a bit more work to do, but it is already a
monster, and I think it would keep make_page_present much cleaner.

Zach

Zach
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