On Wed, Feb 05, 2025 at 10:15:17PM -0800, SeongJae Park wrote:
> Optimize redundant mmap lock operations from process_madvise() by
> directly doing the mmap locking first, and then the remaining works for
> all ranges in the loop.
>
> Reviewed-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
> Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
But please fixup the comment as below. Maybe Andrew could do it if I am
giving enough info to go on, otherwise it could be a quick fix-patch? I
attach a lazy attempt at a fix-patch in case that's useful.
> ---
> mm/madvise.c | 26 ++++++++++++++++++++++++--
> 1 file changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 31e5df75b926..5a0a1fc99d27 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1754,9 +1754,26 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
>
> total_len = iov_iter_count(iter);
>
> + ret = madvise_lock(mm, behavior);
> + if (ret)
> + return ret;
> +
> while (iov_iter_count(iter)) {
> - ret = do_madvise(mm, (unsigned long)iter_iov_addr(iter),
> - iter_iov_len(iter), behavior);
> + unsigned long start = (unsigned long)iter_iov_addr(iter);
> + size_t len_in = iter_iov_len(iter);
> + size_t len;
> +
> + if (!is_valid_madvise(start, len_in, behavior)) {
> + ret = -EINVAL;
> + break;
> + }
> +
> + len = PAGE_ALIGN(len_in);
> + if (start + len == start)
> + ret = 0;
> + else
> + ret = madvise_do_behavior(mm, start, len_in, len,
> + behavior);
> /*
> * An madvise operation is attempting to restart the syscall,
> * but we cannot proceed as it would not be correct to repeat
This comment is now incorrect, please fix up the 2nd paragraph so it is
something like:
/*
* An madvise operation is attempting to restart the syscall,
* but we cannot proceed as it would not be correct to repeat
* the operation in aggregate, and would be surprising to the
* user.
*
* We drop and reacquire locks so it is safe to just loop and
* try again. We check for fatal signals in case we need exit
* early anyway.
*/
See below fixpatch if that's easier...
> @@ -1772,12 +1789,17 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
> ret = -EINTR;
> break;
> }
> +
> + /* Drop and reacquire lock to unwind race. */
> + madvise_unlock(mm, behavior);
> + madvise_lock(mm, behavior);
Thanks for adding!
> continue;
> }
> if (ret < 0)
> break;
> iov_iter_advance(iter, iter_iov_len(iter));
> }
> + madvise_unlock(mm, behavior);
>
> ret = (total_len - iov_iter_count(iter)) ? : ret;
>
> --
> 2.39.5
For convenience I attach a lazy, untested fixpatch which may or may not work :)
----8<----
