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Date: Fri, 11 Mar 2016 14:05:45 +0100
Message-ID: <CAG_fn=UFB3UYg0-uw4TUJvuvu9ZkqqTKG4enMFMXyWC-q65SeA@mail.gmail.com>
Subject: Re: [PATCH v5 2/7] mm, kasan: SLAB support
From: Alexander Potapenko <glider@google.com>
To: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Andrey Konovalov <adech.fo@gmail.com>, Christoph Lameter <cl@linux.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, JoonSoo Kim <js1304@gmail.com>,
        Kostya Serebryany <kcc@google.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>
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On Fri, Mar 11, 2016 at 12:47 PM, Andrey Ryabinin
<ryabinin.a.a@gmail.com> wrote:
> 2016-03-09 14:05 GMT+03:00 Alexander Potapenko <glider@google.com>:
>
>> +struct kasan_track {
>> +       u64 cpu : 6;                    /* for NR_CPUS = 64 */
>
> What about NR_CPUS > 64 ?
After a discussion with Dmitry we've decided to drop |cpu| and |when|
at all, as they do not actually help debugging.
This way we'll make kasan_track only 8 bytes (4 bytes for PID, 4 bytes
for stack handle).
Then the meta structures will be smaller and have nice alignment:

struct kasan_track {
        u32 pid;
        depot_stack_handle_t stack;
};

struct kasan_alloc_meta {
        struct kasan_track track;
        u32 state : 2;  /* enum kasan_state */
        u32 alloc_size : 30;
        u32 reserved;  /* we can use it to store an additional stack
handle, e.g. for debugging RCU */
};

struct kasan_free_meta {
        /* This field is used while the object is in the quarantine.
         * Otherwise it might be used for the allocator freelist.
         */
        void **quarantine_link;
        struct kasan_track track;
};


>> +       u64 pid : 16;                   /* 65536 processes */
>> +       u64 when : 42;                  /* ~140 years */
>> +};
>> +


-- 
Alexander Potapenko
Software Engineer

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