Re: [PATCH v2] udmabuf: use kmem_cache to alloc udmabuf folio

[Huan Yang]

在 2024/7/31 14:26, Huan Yang 写道:

The current udmabuf_folio contains a list_head and the corresponding
folio pointer, with a size of 24 bytes. udmabuf_folio uses kmalloc to
allocate memory.

However, kmalloc is a public pool, starting from 64 bytes. This means
that each udmabuf_folio allocation will waste 40 bytes.

The description here is incorrect. kmalloc pool is 8 16 32, and so on.

So, each udmabuf_folio(24bytes) use kmalloc will waste 8bytes, not 40.

Considering that each udmabuf creates a folio corresponding to a
udmabuf_folio, the wasted memory can be significant in the case of
memory fragmentation.

Furthermore, if udmabuf is frequently used, the allocation and
deallocation of udmabuf_folio will also be frequent.

Therefore, this patch adds a kmem_cache dedicated to the allocation and
deallocation of udmabuf_folio.This is expected to improve the
performance of allocation and deallocation within the expected range,
while also avoiding memory waste.

Signed-off-by: Huan Yang <l...@vivo.com>
---
v2 -> v1: fix double unregister, remove unlikely

  drivers/dma-buf/udmabuf.c | 19 +++++++++++++++----
  1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 047c3cd2ceff..c112c58ef09a 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -24,6 +24,8 @@ static int size_limit_mb = 64;
  module_param(size_limit_mb, int, 0644);
  MODULE_PARM_DESC(size_limit_mb, "Max size of a dmabuf, in megabytes. Default is 
64.");

+static struct kmem_cache *udmabuf_folio_cachep;

+
  struct udmabuf {
        pgoff_t pagecount;
        struct folio **folios;
@@ -169,7 +171,7 @@ static void unpin_all_folios(struct list_head *unpin_list)
                unpin_folio(ubuf_folio->folio);

list_del(&ubuf_folio->list);

-               kfree(ubuf_folio);
+               kmem_cache_free(udmabuf_folio_cachep, ubuf_folio);
        }
  }

@@ -178,7 +180,7 @@ static int add_to_unpin_list(struct list_head *unpin_list,

  {
        struct udmabuf_folio *ubuf_folio;

- ubuf_folio = kzalloc(sizeof(*ubuf_folio), GFP_KERNEL);

+       ubuf_folio = kmem_cache_alloc(udmabuf_folio_cachep, GFP_KERNEL);
        if (!ubuf_folio)
                return -ENOMEM;

@@ -491,11 +493,20 @@ static int __init udmabuf_dev_init(void)

                                           DMA_BIT_MASK(64));
        if (ret < 0) {
                pr_err("Could not setup DMA mask for udmabuf device\n");
-               misc_deregister(&udmabuf_misc);
-               return ret;
+               goto err;
+       }
+
+       udmabuf_folio_cachep = KMEM_CACHE(udmabuf_folio, 0);
+       if (!udmabuf_folio_cachep) {
+               ret = -ENOMEM;
+               goto err;
        }

return 0;

+
+err:
+       misc_deregister(&udmabuf_misc);
+       return ret;
  }

static void __exit udmabuf_dev_exit(void)

base-commit: cd19ac2f903276b820f5d0d89de0c896c27036ed