On Thu, Mar 31, 2022 at 11:01 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Mon, Feb 28, 2022 at 08:21:22PM +0800, Muchun Song wrote:
> > @@ -586,27 +508,48 @@ int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
> > }
> > }
> >
> > + xas_lock_irqsave(&xas, flags);
> > while (i--) {
> > + int index = READ_ONCE(table[i].memcg->kmemcg_id);
> > struct list_lru_per_memcg *mlru = table[i].mlru;
> >
> > + xas_set(&xas, index);
> > +retry:
> > + if (unlikely(index < 0 || xas_error(&xas) || xas_load(&xas))) {
> > kfree(mlru);
> > + } else {
> > + xas_store(&xas, mlru);
> > + if (xas_error(&xas) == -ENOMEM) {
> > + xas_unlock_irqrestore(&xas, flags);
> > + if (xas_nomem(&xas, gfp))
> > + xas_set_err(&xas, 0);
> > + xas_lock_irqsave(&xas, flags);
> > + /*
> > + * The xas lock has been released, this memcg
> > + * can be reparented before us. So reload
> > + * memcg id. More details see the comments
> > + * in memcg_reparent_list_lrus().
> > + */
> > + index = READ_ONCE(table[i].memcg->kmemcg_id);
> > + if (index < 0)
> > + xas_set_err(&xas, 0);
> > + else if (!xas_error(&xas) && index != xas.xa_index)
> > + xas_set(&xas, index);
> > + goto retry;
> > + }
> > + }
> > }
> > + /* xas_nomem() is used to free memory instead of memory allocation. */
> > + if (xas.xa_alloc)
> > + xas_nomem(&xas, gfp);
> > + xas_unlock_irqrestore(&xas, flags);
> > kfree(table);
> >
> > + return xas_error(&xas);
> > }
>
> This is really unidiomatic. And so much more complicated than it needs
> to be.
>
> while (i--) {
> do {
> int index = READ_ONCE(table[i].memcg->kmemcg_id);
> struct list_lru_per_memcg *mlru = table[i].mlru;
>
> xas_set(&xas, index);
> xas_lock_irqsave(&xas, flags);
> if (index < 0 || xas_load(&xas))
> xas_set_err(&xas, -EBUSY);
> xas_store(&xas, mlru);
> if (!xas_error(&xas))
> break;
> xas_unlock_irqrestore(&xas, flags);
> } while (xas_nomem(&xas, gfp));
>
> if (xas_error(&xas))
> kfree(mlru);
> }
>
> kfree(table);
> return xas_error(&xas);
>
> (you might want to mask out the EBUSY error here)
>
I'm not familiar with xarray APIs. I'll dig deeper to see if this code works
properly. Thanks for your suggestions.
