Re: [PATCH] mm/swap: add function get_total_swap_pages to expose total_swap_pages

[Chunming Zhou]

Discussed with Roger just now, we can try "void si_swapinfo(struct 
sysinfo *val)" function to get the total swap space.

Regards,

David Zhou


On 2018å01æ31æ 16:12, Christian KÃnig wrote:
> Yeah, indeed. But what we could do is to rely on a fixed limit like 
> the Intel driver does and I suggested before.
>
> E.g. don't copy anything into a shmemfile when there is only x MB of 
> swap space left.
>
> Roger can you test that approach once more with your fix for the OOM 
> issues in the page fault handler?
>
> Thanks,
> Christian.
>
> Am 31.01.2018 um 09:08 schrieb He, Roger:
> > ÂÂÂÂI 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@xxxxxxxxxxxxxxxxxxxxx] On 
> > Behalf Of Chunming Zhou
> > Sent: Wednesday, January 31, 2018 3:15 PM
> > To: He, Roger <Hongbo.He@xxxxxxx>; dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > Cc: linux-mm@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Koenig, 
> > Christian <Christian.Koenig@xxxxxxx>
> > 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 2018å01æ29æ 16:29, Roger He wrote:
> > > ttm module needs it to determine its internal parameter setting.
> > >
> > > Signed-off-by: Roger He <Hongbo.He@xxxxxxx>
> > > ---
> > > ÂÂ include/linux/swap.h |Â 6 ++++++
> > > ÂÂ mm/swapfile.cÂÂÂÂÂÂÂ | 15 +++++++++++++++
> > > ÂÂ 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 *);
> > > ÂÂ struct backing_dev_info;
> > > ÂÂ extern int init_swap_address_space(unsigned int type, unsigned 
> > > long nr_pages);
> > > ÂÂ extern void exit_swap_address_space(unsigned int type);
> > > +extern long get_total_swap_pages(void);
> > > ÂÂ ÂÂ #else /* CONFIG_SWAP */
> > > ÂÂ @@ -516,6 +517,11 @@ static inline void show_swap_cache_info(void)
> > > ÂÂ {
> > > ÂÂ }
> > > ÂÂ +long get_total_swap_pages(void)
> > > +{
> > > +ÂÂÂ return 0;
> > > +}
> > > +
> > > ÂÂ #define free_swap_and_cache(e) ({(is_migration_entry(e) || 
> > > is_device_private_entry(e));})
> > > ÂÂ #define swapcache_prepare(e) ({(is_migration_entry(e) || 
> > > is_device_private_entry(e));})
> > > ÂÂ 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);
> > > ÂÂ ÂÂ atomic_t nr_rotate_swap = ATOMIC_INIT(0);
> > > ÂÂ +/*
> > > + * expose this value for others use
> > > + */
> > > +long get_total_swap_pages(void)
> > > +{
> > > +ÂÂÂ long ret;
> > > +
> > > +ÂÂÂ spin_lock(&swap_lock);
> > > +ÂÂÂ ret = total_swap_pages;
> > > +ÂÂÂ spin_unlock(&swap_lock);
> > > +
> > > +ÂÂÂ return ret;
> > > +}
> > > +EXPORT_SYMBOL_GPL(get_total_swap_pages);
> > > +
> > > ÂÂ static inline unsigned char swap_count(unsigned char ent)
> > > ÂÂ {
> > > ÂÂÂÂÂÂ return ent & ~SWAP_HAS_CACHE;ÂÂÂ /* may include SWAP_HAS_CONT 
> > > flag */
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