Re: [Qemu-devel] [PATCH 01/17] mm: gup: add FOLL_TRIED

[Paolo Bonzini]

> This needs more explanation than that one-liner comment. Make the
> commit message explain why the new FOLL_TRIED flag exists.

This patch actually is extracted from a 3.18 commit in the KVM tree,
https://git.kernel.org/cgit/virt/kvm/kvm.git/commit/?h=next&id=234b239b.

Here is how that patch uses the flag:

    /*
     * The previous call has now waited on the IO. Now we can
     * retry and complete. Pass TRIED to ensure we do not re
     * schedule async IO (see e.g. filemap_fault).
     */
    down_read(&mm->mmap_sem);
    npages = __get_user_pages(tsk, mm, addr, 1, flags | FOLL_TRIED,
                              pagep, NULL, NULL);