netdev - Re: [PATCH v3 net-next 00/23] net: add preliminary netdev refcount tracking

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Date:   Wed, 8 Dec 2021 10:53:45 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v3 net-next 00/23] net: add preliminary netdev refcount tracking

On Wed, Dec 8, 2021 at 10:21 AM Eric Dumazet <edumazet@...gle.com> wrote:
>

> I do not think ns precision of a ktime_t is really needed.
>
> jiffies should be enough, saving potential high cost of ktime_get_ns()
>

Also worth mentioning this is doubling size of ref_tracker.
(going from 32-byte to 64-bytes standard kmem cache)

I would advise creating a dedicated kmem_cache to avoid wasting memory.

current layout being:

struct ref_tracker {
 struct list_head           head;                 /*     0  0x10 */
 bool                       dead;                 /*  0x10   0x1 */

 /* XXX 3 bytes hole, try to pack */

 depot_stack_handle_t       alloc_stack_handle;   /*  0x14   0x4 */
 depot_stack_handle_t       free_stack_handle;    /*  0x18   0x4 */

 /* size: 32, cachelines: 1, members: 4 */
 /* sum members: 25, holes: 1, sum holes: 3 */
 /* padding: 4 */
 /* last cacheline: 32 bytes */
};