Re: [RFC PATCH v2 4/4] mm/madvise: remove redundant mmap_lock operations from process_madvise()

[Davidlohr Bueso]

On Fri, 31 Jan 2025, Lorenzo Stoakes wrote:

> On Thu, Jan 16, 2025 at 05:30:58PM -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.
> >
> > Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
>
> I wonder if this might increase lock contention because now all of the
> vector operations will hold the relevant mm lock without releasing after
> each operation?

That was exactly my concern. While afaict the numbers presented in v1
are quite nice, this is ultimately a micro-benchmark, where no other
unrelated threads are impacted by these new hold times.

> Probably it's ok given limited size of iov, but maybe in future we'd want
> to set a limit on the ranges before we drop/reacquire lock?

imo, this should best be done in the same patch/series. Maybe extend
the benchmark to use IOV_MAX and find a sweet spot?

Thanks,
Davidlohr