On Wed, Feb 22, 2023 at 12:06:20PM -0500, Johannes Weiner wrote:
Hello,
On Tue, Feb 21, 2023 at 04:43:44PM -0500, Peter Xu wrote:
If memory charge failed, the caller shouldn't call mem_cgroup_uncharge(). Let alloc_charge_hpage() handle the error itself and clear hpage properly if mem charge fails.
I'm a bit confused by this patch.
There isn't anything wrong with calling mem_cgroup_uncharge() on an uncharged page, functionally. It checks and bails out.
Indeed, I didn't really notice there's zero side effect of calling that, sorry. In that case both "Fixes" and "Cc: stable" do not apply.
It's an unnecessary call of course, but since it's an error path it's also not a cost issue, either.
I could see an argument for improving the code, but this is actually more code, and the caller still has the uncharge-and-put branch anyway for when the collapse fails later on.
So I'm not sure I understand the benefit of this change.
Yes, the benefit is having a clear interface for alloc_charge_hpage() with no prone to leaking huge page.
The patch comes from a review for David's other patch here:
https://lore.kernel.org/all/Y%2FU9fBxVJdhxiZ1v@x1n/
I've attached a new version just to reword and remove the inproper tags. Do you think that's acceptable?
Thanks,