linux-kernel - Re: [PATCH v2] memcg: replace memcg ID idr with xarray

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Message-ID: <Zr8LbVe8IGd1JSQo@tiehlicka>
Date: Fri, 16 Aug 2024 10:18:53 +0200
From: Michal Hocko <mhocko@...e.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Matthew Wilcox <willy@...radead.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Johannes Weiner <hannes@...xchg.org>,
	Muchun Song <muchun.song@...ux.dev>,
	"T . J . Mercier" <tjmercier@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH v2] memcg: replace memcg ID idr with xarray

On Fri 16-08-24 00:43:34, Andrew Morton wrote:
> On Fri, 16 Aug 2024 09:19:58 +0200 Michal Hocko <mhocko@...e.com> wrote:
> 
> > On Thu 15-08-24 22:16:27, Matthew Wilcox wrote:
> > > On Thu, Aug 15, 2024 at 07:31:43PM +0000, Roman Gushchin wrote:
> > > > There is another subtle change here: xa_alloc() returns -EBUSY in the case
> > > > of the address space exhaustion, while the old code returned -ENOSPC.
> > > > It's unlikely a big practical problem.
> > > 
> > > I decided that EBUSY was the right errno for this situation;
> > > 
> > > #define EBUSY           16      /* Device or resource busy */
> > > #define ENOSPC          28      /* No space left on device */
> > > 
> > > ENOSPC seemed wrong; the device isn't out of space.
> > 
> > The thing is that this is observable by userspace - mkdir would return a
> > different and potentially unexpected errno. We can try and see whether
> > anybody complains or just translate the error.
> 
> The mkdir(2) manpage doesn't list EBUSY.  Maybe ENOMEM is close enough.

it used to report ENOSPC with xarray.

-- 
Michal Hocko
SUSE Labs