Re: [PATCH] mm/zswap: Fix the compatibility of zsmalloc and zswap

["tiantao (H)" <tiantao6@huawei.com>]

在 2020/12/24 22:16, Vitaly Wool 写道:
> On Thu, Dec 24, 2020 at 1:16 PM Tian Tao <tiantao6@hisilicon.com> wrote:
>> add a flag to zpool, named is "can_sleep_mapped", and have it set true
>> for zbud/z3fold, set false for zsmalloc. Then zswap could go the current
>> path if the flag is true; and if it's false, copy data from src to a
>> temporary buffer, then unmap the handle, take the mutex, process the
>> buffer instead of src to avoid sleeping function called from atomic
>> context.
>>
>> Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
>> ---
>>   include/linux/zpool.h |  2 ++
>>   mm/z3fold.c           |  1 +
>>   mm/zbud.c             |  1 +
>>   mm/zpool.c            | 13 +++++++++++++
>>   mm/zsmalloc.c         |  1 +
>>   mm/zswap.c            | 23 +++++++++++++++++++++--
>>   6 files changed, 39 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/zpool.h b/include/linux/zpool.h
>> index 51bf430..a354f4fe 100644
>> --- a/include/linux/zpool.h
>> +++ b/include/linux/zpool.h
>> @@ -82,6 +82,7 @@ u64 zpool_get_total_size(struct zpool *pool);
>>    */
>>   struct zpool_driver {
>>          char *type;
>> +       bool sleep_mapped;
> Could you please add this somewhat further down, close to  map / unmap
> callbacks, and add a description of the field above, too?
>>          struct module *owner;
>>          atomic_t refcount;
>>          struct list_head list;
>> @@ -112,5 +113,6 @@ void zpool_register_driver(struct zpool_driver *driver);
>>   int zpool_unregister_driver(struct zpool_driver *driver);
>>
>>   bool zpool_evictable(struct zpool *pool);
>> +bool zpool_can_sleep_mapped(struct zpool *pool);
>>
>>   #endif
>> diff --git a/mm/z3fold.c b/mm/z3fold.c
>> index dacb0d7..234b46f 100644
>> --- a/mm/z3fold.c
>> +++ b/mm/z3fold.c
>> @@ -1778,6 +1778,7 @@ static u64 z3fold_zpool_total_size(void *pool)
>>
>>   static struct zpool_driver z3fold_zpool_driver = {
>>          .type =         "z3fold",
>> +       .sleep_mapped = true,
>>          .owner =        THIS_MODULE,
>>          .create =       z3fold_zpool_create,
>>          .destroy =      z3fold_zpool_destroy,
>> diff --git a/mm/zbud.c b/mm/zbud.c
>> index c49966e..7ec5f27 100644
>> --- a/mm/zbud.c
>> +++ b/mm/zbud.c
>> @@ -203,6 +203,7 @@ static u64 zbud_zpool_total_size(void *pool)
>>
>>   static struct zpool_driver zbud_zpool_driver = {
>>          .type =         "zbud",
>> +       .sleep_mapped = true,
>>          .owner =        THIS_MODULE,
>>          .create =       zbud_zpool_create,
>>          .destroy =      zbud_zpool_destroy,
>> diff --git a/mm/zpool.c b/mm/zpool.c
>> index 3744a2d..5ed7120 100644
>> --- a/mm/zpool.c
>> +++ b/mm/zpool.c
>> @@ -23,6 +23,7 @@ struct zpool {
>>          void *pool;
>>          const struct zpool_ops *ops;
>>          bool evictable;
>> +       bool can_sleep_mapped;
>>
>>          struct list_head list;
>>   };
>> @@ -183,6 +184,7 @@ struct zpool *zpool_create_pool(const char *type, const char *name, gfp_t gfp,
>>          zpool->pool = driver->create(name, gfp, ops, zpool);
>>          zpool->ops = ops;
>>          zpool->evictable = driver->shrink && ops && ops->evict;
>> +       zpool->can_sleep_mapped = driver->sleep_mapped;
>>
>>          if (!zpool->pool) {
>>                  pr_err("couldn't create %s pool\n", type);
>> @@ -393,6 +395,17 @@ bool zpool_evictable(struct zpool *zpool)
>>          return zpool->evictable;
>>   }
>>
>> +/**
>> + * zpool_can_sleep_mapped - Test if zpool can sleep when do mapped.
>> + * @zpool:     The zpool to test
>> + *
>> + * Returns: true if zpool can sleep; false otherwise.
>> + */
>> +bool zpool_can_sleep_mapped(struct zpool *zpool)
>> +{
>> +       return zpool->can_sleep_mapped;
>> +}
>> +
>>   MODULE_LICENSE("GPL");
>>   MODULE_AUTHOR("Dan Streetman <ddstreet@ieee.org>");
>>   MODULE_DESCRIPTION("Common API for compressed memory storage");
>> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
>> index 7289f50..a991d3c 100644
>> --- a/mm/zsmalloc.c
>> +++ b/mm/zsmalloc.c
>> @@ -440,6 +440,7 @@ static u64 zs_zpool_total_size(void *pool)
>>
>>   static struct zpool_driver zs_zpool_driver = {
>>          .type =                   "zsmalloc",
>> +       .sleep_mapped =           false,
> You don't have to add this, it will be false if not explicitly specified.
>
>>          .owner =                  THIS_MODULE,
>>          .create =                 zs_zpool_create,
>>          .destroy =                zs_zpool_destroy,
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index 182f6ad..51b033a 100644
>> --- a/mm/zswap.c
>> +++ b/mm/zswap.c
>> @@ -1235,7 +1235,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>>          struct zswap_entry *entry;
>>          struct scatterlist input, output;
>>          struct crypto_acomp_ctx *acomp_ctx;
>> -       u8 *src, *dst;
>> +       u8 *src, *dst, *tmp;
>>          unsigned int dlen;
>>          int ret;
>>
>> @@ -1256,12 +1256,27 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>>                  goto freeentry;
>>          }
>>
>> +       if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
>> +
>> +               tmp = kzalloc(entry->length, GFP_KERNEL);
> Do we really need kzalloc here? the buffer will be written to in a few
> moments anyway.
> Also, we allocate a small buffer for a short while, and this is likely
> to be a performance critical path, so GFP_ATOMIC looks more
> appropriate.
>
>> +               if (!tmp)
>> +                       return -ENOMEM;
> You can't just return here, you need to call zswap_entry_put() first.
>
> Since this is obviously not the final version of your patch, could you
> please split it in 2 the next time? I'd prefer setting flags to
> specific backends in a separate patch.

Thanks for helping to review the code.

I will post a new patch of my understanding according to you advice, if 
I do not

understand the right,  you can  help point out, I continue to modify

>
> Best regards,
>     Vitaly
>
>> +       }
>> +
>>          /* decompress */
>>          dlen = PAGE_SIZE;
>>          src = zpool_map_handle(entry->pool->zpool, entry->handle, ZPOOL_MM_RO);
>>          if (zpool_evictable(entry->pool->zpool))
>>                  src += sizeof(struct zswap_header);
>>
>> +       if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
>> +
>> +               memcpy(tmp, src, entry->length);
>> +               src = tmp;
>> +
>> +               zpool_unmap_handle(entry->pool->zpool, entry->handle);
>> +       }
>> +
>>          acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
>>          mutex_lock(acomp_ctx->mutex);
>>          sg_init_one(&input, src, entry->length);
>> @@ -1271,7 +1286,11 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>>          ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
>>          mutex_unlock(acomp_ctx->mutex);
>>
>> -       zpool_unmap_handle(entry->pool->zpool, entry->handle);
>> +       if (zpool_can_sleep_mapped(entry->pool->zpool))
>> +               zpool_unmap_handle(entry->pool->zpool, entry->handle);
>> +       else
>> +               kfree(tmp);
>> +
>>          BUG_ON(ret);
>>
>>   freeentry:
>> --
>> 2.7.4
>>
> .
>