[PATCH] drm/ttm: make the pool shrinker lock a mutex

[Daniel Vetter]

On Tue, Jan 12, 2021 at 3:06 PM Christian König
<ckoenig.leichtzumerken at gmail.com> wrote:
>
> Am 12.01.21 um 15:03 schrieb Daniel Vetter:
> > On Mon, Jan 11, 2021 at 2:57 PM Christian König
> > <ckoenig.leichtzumerken at gmail.com> wrote:
> >> set_pages_wb() might sleep and so we can't do this in an atomic context.
> >>
> >> Signed-off-by: Christian König <christian.koenig at amd.com>
> >> Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov at gmail.com>
> >> Fixes: d099fc8f540a ("drm/ttm: new TT backend allocation pool v3")
> > Hm I guess long term proper fix would be to pull the shrinker into two
> > parts, first part takes the right amount of entries of the list,
> > holding the lock. 2nd part does the releasing (or maybe at least in
> > batches). lru locks should be cheap, doing expensive stuff like
> > flushing or rewriting ptes might not be the best idea.
>
> Yeah, agree. It should actually be trivial, but I didn't wanted the
> churn in fixes.
>
> So just going for the easy fix now and the optimal later on.

Makes sense. Maybe add that as an explanation to the commit message,
if you haven't pushed yet. A-b: on the patch.
-Daniel

>
> Regards,
> Christian.
>
> > -Daniel
> >
> >> ---
> >>   drivers/gpu/drm/ttm/ttm_pool.c | 20 ++++++++++----------
> >>   1 file changed, 10 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
> >> index a00b7ab9c14c..6a6eeba423d1 100644
> >> --- a/drivers/gpu/drm/ttm/ttm_pool.c
> >> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
> >> @@ -66,7 +66,7 @@ static struct ttm_pool_type global_uncached[MAX_ORDER];
> >>   static struct ttm_pool_type global_dma32_write_combined[MAX_ORDER];
> >>   static struct ttm_pool_type global_dma32_uncached[MAX_ORDER];
> >>
> >> -static spinlock_t shrinker_lock;
> >> +static struct mutex shrinker_lock;
> >>   static struct list_head shrinker_list;
> >>   static struct shrinker mm_shrinker;
> >>
> >> @@ -249,9 +249,9 @@ static void ttm_pool_type_init(struct ttm_pool_type *pt, struct ttm_pool *pool,
> >>          spin_lock_init(&pt->lock);
> >>          INIT_LIST_HEAD(&pt->pages);
> >>
> >> -       spin_lock(&shrinker_lock);
> >> +       mutex_lock(&shrinker_lock);
> >>          list_add_tail(&pt->shrinker_list, &shrinker_list);
> >> -       spin_unlock(&shrinker_lock);
> >> +       mutex_unlock(&shrinker_lock);
> >>   }
> >>
> >>   /* Remove a pool_type from the global shrinker list and free all pages */
> >> @@ -259,9 +259,9 @@ static void ttm_pool_type_fini(struct ttm_pool_type *pt)
> >>   {
> >>          struct page *p, *tmp;
> >>
> >> -       spin_lock(&shrinker_lock);
> >> +       mutex_lock(&shrinker_lock);
> >>          list_del(&pt->shrinker_list);
> >> -       spin_unlock(&shrinker_lock);
> >> +       mutex_unlock(&shrinker_lock);
> >>
> >>          list_for_each_entry_safe(p, tmp, &pt->pages, lru)
> >>                  ttm_pool_free_page(pt->pool, pt->caching, pt->order, p);
> >> @@ -302,7 +302,7 @@ static unsigned int ttm_pool_shrink(void)
> >>          unsigned int num_freed;
> >>          struct page *p;
> >>
> >> -       spin_lock(&shrinker_lock);
> >> +       mutex_lock(&shrinker_lock);
> >>          pt = list_first_entry(&shrinker_list, typeof(*pt), shrinker_list);
> >>
> >>          p = ttm_pool_type_take(pt);
> >> @@ -314,7 +314,7 @@ static unsigned int ttm_pool_shrink(void)
> >>          }
> >>
> >>          list_move_tail(&pt->shrinker_list, &shrinker_list);
> >> -       spin_unlock(&shrinker_lock);
> >> +       mutex_unlock(&shrinker_lock);
> >>
> >>          return num_freed;
> >>   }
> >> @@ -564,7 +564,7 @@ int ttm_pool_debugfs(struct ttm_pool *pool, struct seq_file *m)
> >>   {
> >>          unsigned int i;
> >>
> >> -       spin_lock(&shrinker_lock);
> >> +       mutex_lock(&shrinker_lock);
> >>
> >>          seq_puts(m, "\t ");
> >>          for (i = 0; i < MAX_ORDER; ++i)
> >> @@ -600,7 +600,7 @@ int ttm_pool_debugfs(struct ttm_pool *pool, struct seq_file *m)
> >>          seq_printf(m, "\ntotal\t: %8lu of %8lu\n",
> >>                     atomic_long_read(&allocated_pages), page_pool_size);
> >>
> >> -       spin_unlock(&shrinker_lock);
> >> +       mutex_unlock(&shrinker_lock);
> >>
> >>          return 0;
> >>   }
> >> @@ -644,7 +644,7 @@ int ttm_pool_mgr_init(unsigned long num_pages)
> >>          if (!page_pool_size)
> >>                  page_pool_size = num_pages;
> >>
> >> -       spin_lock_init(&shrinker_lock);
> >> +       mutex_init(&shrinker_lock);
> >>          INIT_LIST_HEAD(&shrinker_list);
> >>
> >>          for (i = 0; i < MAX_ORDER; ++i) {
> >> --
> >> 2.25.1
> >>
> >> _______________________________________________
> >> dri-devel mailing list
> >> dri-devel at lists.freedesktop.org
> >> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> >
> >
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch