Re: [PATCH v2 3/7] mm/swap: Use local_lock for protection

Ingo Molnar
2020-05-25T06:44:42Z

* Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

> From: Ingo Molnar <mingo@kernel.org>
>
> The various struct pagevec per CPU variables are protected by disabling
> either preemption or interrupts across the critical sections. Inside
> these sections spinlocks have to be acquired.

> diff --git a/mm/swap.c b/mm/swap.c
> index bf9a79fed62d7..4f965292044ca 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -35,6 +35,7 @@
> #include <linux/uio.h>
> #include <linux/hugetlb.h>
> #include <linux/page_idle.h>
> +#include <linux/locallock.h>
>
> #include "internal.h"
>
> @@ -44,14 +45,29 @@
> /* How many pages do we try to swap or page in/out together? */
> int page_cluster;
>
> -static DEFINE_PER_CPU(struct pagevec, lru_add_pvec);
> -static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
> -static DEFINE_PER_CPU(struct pagevec, lru_deactivate_file_pvecs);
> -static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
> -static DEFINE_PER_CPU(struct pagevec, lru_lazyfree_pvecs);
> +/* Protecting lru_rotate_pvecs */
> +struct lru_rotate_pvecs {
> + struct local_lock lock;
> + struct pagevec pvec;
> +};
> +static DEFINE_PER_CPU(struct lru_rotate_pvecs, lru_rotate_pvecs) = {
> + .lock = INIT_LOCAL_LOCK(lock),
> +};
> +
> +/* Protecting the following struct pagevec */
> +struct lru_pvecs {
> + struct local_lock lock;
> + struct pagevec lru_add_pvec;
> + struct pagevec lru_deactivate_file_pvecs;
> + struct pagevec lru_deactivate_pvecs;
> + struct pagevec lru_lazyfree_pvecs;

Ack on coalescing these into the 'struct lru_pvecs' helper structure,
but a minor namespace organization nit: I'd drop the _pvec/_pvecs
postfix from the field names, i.e. make it something like this:

/* Protecting the following struct pagevec */
struct lru_pvecs {
struct local_lock lock;
struct pagevec lru_add;
struct pagevec lru_deactivate_file;
struct pagevec lru_deactivate;
struct pagevec lru_lazyfree;

With that change, usage is a straightforward:

pvec->lru_deactivate

instead of the double-pvec name:

pvec->lru_deactivate_pvec

> + local_lock_irqsave(&lru_rotate_pvecs.lock, flags);

Also:

> + pvec = this_cpu_ptr(&lru_rotate_pvecs.pvec);

s/lru_rotate_pvecs
/lru_rotate_pvec

it's a single pagevec, using plural is confusing when reading the
code.

I'd also suggest adding a comment explaining why the lru_rotate_pvec
local lock is split away from lru_add/deactivate/deactivate/lazyfree
pagevec local lock.

Thanks,

Ingo