On Wed, Feb 22, 2023 at 12:38:36PM -0500, Peter Xu wrote: > 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/ Ah, that makes sense. Thanks for the context. > From 0595acbd688b60ff7b2821a073c0fe857a4ae0ee Mon Sep 17 00:00:00 2001 > From: Peter Xu <peterx@xxxxxxxxxx> > Date: Tue, 21 Feb 2023 16:43:44 -0500 > Subject: [PATCH] mm/khugepaged: alloc_charge_hpage() take care of mem charge > errors > > If memory charge failed, instead of returning the hpage but with an error, > allow the function to cleanup the folio properly, which is normally what a > function should do in this case - either return successfully, or return > with no side effect of partial runs with an indicated error. > > This will also avoid the caller calling mem_cgroup_uncharge() unnecessarily > with either anon or shmem path (even if it's safe to do so). > > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Yang Shi <shy828301@xxxxxxxxx> > Cc: David Stevens <stevensd@xxxxxxxxxxxx> > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
