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    SubjectRE: [PATCH] mm/swap: add function get_total_swap_pages to expose total_swap_pages
    Date
    	I think this patch isn't need at all. You can directly read total_swap_pages variable in TTM.

    Because the variable is not exported by EXPORT_SYMBOL_GPL. So direct using will result in:
    "WARNING: "total_swap_pages" [drivers/gpu/drm/ttm/ttm.ko] undefined!".

    Thanks
    Roger(Hongbo.He)
    -----Original Message-----
    From: dri-devel [mailto:dri-devel-bounces@lists.freedesktop.org] On Behalf Of Chunming Zhou
    Sent: Wednesday, January 31, 2018 3:15 PM
    To: He, Roger <Hongbo.He@amd.com>; dri-devel@lists.freedesktop.org
    Cc: linux-mm@kvack.org; linux-kernel@vger.kernel.org; Koenig, Christian <Christian.Koenig@amd.com>
    Subject: Re: [PATCH] mm/swap: add function get_total_swap_pages to expose total_swap_pages

    Hi Roger,

    I think this patch isn't need at all. You can directly read total_swap_pages variable in TTM. See the comment:

    /* protected with swap_lock. reading in vm_swap_full() doesn't need lock */ long total_swap_pages;

    there are many places using it directly, you just couldn't change its value. Reading it doesn't need lock.


    Regards,

    David Zhou


    On 2018年01月29日 16:29, Roger He wrote:
    > ttm module needs it to determine its internal parameter setting.
    >
    > Signed-off-by: Roger He <Hongbo.He@amd.com>
    > ---
    > include/linux/swap.h | 6 ++++++
    > mm/swapfile.c | 15 +++++++++++++++
    > 2 files changed, 21 insertions(+)
    >
    > diff --git a/include/linux/swap.h b/include/linux/swap.h
    > index c2b8128..708d66f 100644
    > --- a/include/linux/swap.h
    > +++ b/include/linux/swap.h
    > @@ -484,6 +484,7 @@ extern int try_to_free_swap(struct page *);
    > struct backing_dev_info;
    > extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
    > extern void exit_swap_address_space(unsigned int type);
    > +extern long get_total_swap_pages(void);
    >
    > #else /* CONFIG_SWAP */
    >
    > @@ -516,6 +517,11 @@ static inline void show_swap_cache_info(void)
    > {
    > }
    >
    > +long get_total_swap_pages(void)
    > +{
    > + return 0;
    > +}
    > +
    > #define free_swap_and_cache(e) ({(is_migration_entry(e) || is_device_private_entry(e));})
    > #define swapcache_prepare(e) ({(is_migration_entry(e) || is_device_private_entry(e));})
    >
    > diff --git a/mm/swapfile.c b/mm/swapfile.c
    > index 3074b02..a0062eb 100644
    > --- a/mm/swapfile.c
    > +++ b/mm/swapfile.c
    > @@ -98,6 +98,21 @@ static atomic_t proc_poll_event = ATOMIC_INIT(0);
    >
    > atomic_t nr_rotate_swap = ATOMIC_INIT(0);
    >
    > +/*
    > + * expose this value for others use
    > + */
    > +long get_total_swap_pages(void)
    > +{
    > + long ret;
    > +
    > + spin_lock(&swap_lock);
    > + ret = total_swap_pages;
    > + spin_unlock(&swap_lock);
    > +
    > + return ret;
    > +}
    > +EXPORT_SYMBOL_GPL(get_total_swap_pages);
    > +
    > static inline unsigned char swap_count(unsigned char ent)
    > {
    > return ent & ~SWAP_HAS_CACHE; /* may include SWAP_HAS_CONT flag */

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