Re: [PATCH v3 1/2] mm: introduce process_mrelease system call

On Fri 23-07-21 01:11:51, Suren Baghdasaryan wrote:

On Thu, Jul 22, 2021, 11:20 PM Michal Hocko [off-list ref] wrote:

quoted

On Thu 22-07-21 21:47:56, Suren Baghdasaryan wrote:

quoted

On Thu, Jul 22, 2021, 7:04 PM Shakeel Butt [off-list ref] wrote:

quoted

On Thu, Jul 22, 2021 at 6:14 PM Suren Baghdasaryan [off-list ref]
wrote:

quoted

[...]

quoted

+
+       mmap_read_lock(mm);

How about mmap_read_trylock(mm) and return -EAGAIN on failure?

That sounds like a good idea. Thanks! I'll add that in the next respin.

Why is that a good idea? Can you do anything meaningful about the
failure other than immediately retry the syscall and hope for the best?

I was thinking if this syscall implements "best effort without blocking"
approach then for a more strict usage user can simply retry.

I do not think we really want to promise non blocking behavior at this
stage unless that is absolutely necessary. The current implementation
goes an extra mile to not block but I wouldn't carve it into stone via
userspace expectations.

However
retrying means issuing another syscall, so additional overhead...
I guess such "best effort" approach would be unusual for a syscall, so
maybe we can keep it as it is now and if such "do not block" mode is needed
we can use flags to implement it later?

Yeah, an explicit opt-in via flags would be an option if that turns out
to be really necessary.
-- 
Michal Hocko
SUSE Labs