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Message-ID: <63dc1d86-2a15-6b7e-f63a-63fccb25eae2@bytedance.com>
Date: Wed, 23 Aug 2023 10:59:34 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: daniel@...ll.ch
Cc: akpm@...ux-foundation.org, david@...morbit.com, tkhai@...ru,
vbabka@...e.cz, roman.gushchin@...ux.dev, djwong@...nel.org,
brauner@...nel.org, paulmck@...nel.org, tytso@....edu,
steven.price@....com, cel@...nel.org, senozhatsky@...omium.org,
yujie.liu@...el.com, gregkh@...uxfoundation.org,
muchun.song@...ux.dev, simon.horman@...igine.com,
dlemoal@...nel.org, kvm@...r.kernel.org,
dri-devel@...ts.freedesktop.org,
virtualization@...ts.linux-foundation.org, linux-mm@...ck.org,
dm-devel@...hat.com, linux-mtd@...ts.infradead.org, x86@...nel.org,
cluster-devel@...hat.com, xen-devel@...ts.xenproject.org,
linux-ext4@...r.kernel.org, linux-arm-msm@...r.kernel.org,
rcu@...r.kernel.org, linux-bcache@...r.kernel.org,
Muchun Song <songmuchun@...edance.com>,
linux-raid@...r.kernel.org, linux-nfs@...r.kernel.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net, linux-xfs@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-erofs@...ts.ozlabs.org,
linux-btrfs@...r.kernel.org, daniel.vetter@...ll.ch
Subject: Re: [PATCH v4 43/48] drm/ttm: introduce pool_shrink_rwsem
Hi Daniel,
On 2023/8/22 21:56, Daniel Vetter wrote:
> On Mon, Aug 07, 2023 at 07:09:31PM +0800, Qi Zheng wrote:
>> Currently, the synchronize_shrinkers() is only used by TTM pool. It only
>> requires that no shrinkers run in parallel.
>>
>> After we use RCU+refcount method to implement the lockless slab shrink,
>> we can not use shrinker_rwsem or synchronize_rcu() to guarantee that all
>> shrinker invocations have seen an update before freeing memory.
>>
>> So we introduce a new pool_shrink_rwsem to implement a private
>> synchronize_shrinkers(), so as to achieve the same purpose.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
>> Reviewed-by: Muchun Song <songmuchun@...edance.com>
>
> On the 5 drm patches (I counted 2 ttm and 3 drivers) for merging through
> some other tree (since I'm assuming that's how this will land):
Yeah, there are 5 drm patches: PATCH v4 07/48 23/48 24/48 25/48 43/48.
>
> Acked-by: Daniel Vetter <daniel.vetter@...ll.ch>
Thanks for your review!
Qi
>
>> ---
>> drivers/gpu/drm/ttm/ttm_pool.c | 15 +++++++++++++++
>> include/linux/shrinker.h | 2 --
>> mm/shrinker.c | 15 ---------------
>> 3 files changed, 15 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
>> index c9c9618c0dce..38b4c280725c 100644
>> --- a/drivers/gpu/drm/ttm/ttm_pool.c
>> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
>> @@ -74,6 +74,7 @@ static struct ttm_pool_type global_dma32_uncached[MAX_ORDER + 1];
>> static spinlock_t shrinker_lock;
>> static struct list_head shrinker_list;
>> static struct shrinker *mm_shrinker;
>> +static DECLARE_RWSEM(pool_shrink_rwsem);
>>
>> /* Allocate pages of size 1 << order with the given gfp_flags */
>> static struct page *ttm_pool_alloc_page(struct ttm_pool *pool, gfp_t gfp_flags,
>> @@ -317,6 +318,7 @@ static unsigned int ttm_pool_shrink(void)
>> unsigned int num_pages;
>> struct page *p;
>>
>> + down_read(&pool_shrink_rwsem);
>> spin_lock(&shrinker_lock);
>> pt = list_first_entry(&shrinker_list, typeof(*pt), shrinker_list);
>> list_move_tail(&pt->shrinker_list, &shrinker_list);
>> @@ -329,6 +331,7 @@ static unsigned int ttm_pool_shrink(void)
>> } else {
>> num_pages = 0;
>> }
>> + up_read(&pool_shrink_rwsem);
>>
>> return num_pages;
>> }
>> @@ -572,6 +575,18 @@ void ttm_pool_init(struct ttm_pool *pool, struct device *dev,
>> }
>> EXPORT_SYMBOL(ttm_pool_init);
>>
>> +/**
>> + * synchronize_shrinkers - Wait for all running shrinkers to complete.
>> + *
>> + * This is useful to guarantee that all shrinker invocations have seen an
>> + * update, before freeing memory, similar to rcu.
>> + */
>> +static void synchronize_shrinkers(void)
>> +{
>> + down_write(&pool_shrink_rwsem);
>> + up_write(&pool_shrink_rwsem);
>> +}
>> +
>> /**
>> * ttm_pool_fini - Cleanup a pool
>> *
>> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
>> index c55c07c3f0cb..025c8070dd86 100644
>> --- a/include/linux/shrinker.h
>> +++ b/include/linux/shrinker.h
>> @@ -103,8 +103,6 @@ struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...);
>> void shrinker_register(struct shrinker *shrinker);
>> void shrinker_free(struct shrinker *shrinker);
>>
>> -extern void synchronize_shrinkers(void);
>> -
>> #ifdef CONFIG_SHRINKER_DEBUG
>> extern int __printf(2, 3) shrinker_debugfs_rename(struct shrinker *shrinker,
>> const char *fmt, ...);
>> diff --git a/mm/shrinker.c b/mm/shrinker.c
>> index 3ab301ff122d..a27779ed3798 100644
>> --- a/mm/shrinker.c
>> +++ b/mm/shrinker.c
>> @@ -650,18 +650,3 @@ void shrinker_free(struct shrinker *shrinker)
>> kfree(shrinker);
>> }
>> EXPORT_SYMBOL_GPL(shrinker_free);
>> -
>> -/**
>> - * synchronize_shrinkers - Wait for all running shrinkers to complete.
>> - *
>> - * This is equivalent to calling unregister_shrink() and register_shrinker(),
>> - * but atomically and with less overhead. This is useful to guarantee that all
>> - * shrinker invocations have seen an update, before freeing memory, similar to
>> - * rcu.
>> - */
>> -void synchronize_shrinkers(void)
>> -{
>> - down_write(&shrinker_rwsem);
>> - up_write(&shrinker_rwsem);
>> -}
>> -EXPORT_SYMBOL(synchronize_shrinkers);
>> --
>> 2.30.2
>>
>
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