Hi Huan,
> Subject: [PATCH v6 7/7] udmabuf: reuse folio array when pin folios
>
> When invoke memfd_pin_folios, we need offer an array to save each folio
> which we pinned.
>
> The currently way is dynamic alloc an array, get folios, save into
*current
> udmabuf and then free.
>
> If the size is tiny(alloc from slab) is ok due to slab can cache it.
> Or, just PCP order can cover, also ok.
A casual reader may not know what is PCP. Please mention what it
stands for and how it is relevant here.
>
> But if size is huge, need fallback into vmalloc, then, not well, due to
> each page need alloc, and map into vmalloc area. Too heavy.
I think it would be better if the above two lines are rewritten to more clearly
describe why or how fallback to vmalloc adversely affects performance.
Thanks,
Vivek
>
> Now that we need to iter each udmabuf item, then pin it's range folios,
> we can reuse the maximum size range's folios array.
>
> Signed-off-by: Huan Yang <link@xxxxxxxx>
> Acked-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
> ---
> drivers/dma-buf/udmabuf.c | 36 +++++++++++++++++++++---------------
> 1 file changed, 21 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index 0e405a589ca2..9fc5d22d54ae 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -341,28 +341,20 @@ static int export_udmabuf(struct udmabuf *ubuf,
> }
>
> static long udmabuf_pin_folios(struct udmabuf *ubuf, struct file *memfd,
> - loff_t start, loff_t size)
> + loff_t start, loff_t size, struct folio **folios)
> {
> pgoff_t nr_pinned = ubuf->nr_pinned;
> pgoff_t upgcnt = ubuf->pagecount;
> - struct folio **folios = NULL;
> u32 cur_folio, cur_pgcnt;
> pgoff_t pgoff, pgcnt;
> long nr_folios;
> - long ret = 0;
> loff_t end;
>
> pgcnt = size >> PAGE_SHIFT;
> - folios = kvmalloc_array(pgcnt, sizeof(*folios), GFP_KERNEL);
> - if (!folios)
> - return -ENOMEM;
> -
> end = start + (pgcnt << PAGE_SHIFT) - 1;
> nr_folios = memfd_pin_folios(memfd, start, end, folios, pgcnt,
> &pgoff);
> - if (nr_folios <= 0) {
> - ret = nr_folios ? nr_folios : -EINVAL;
> - goto end;
> - }
> + if (nr_folios <= 0)
> + return nr_folios ? nr_folios : -EINVAL;
>
> cur_pgcnt = 0;
> for (cur_folio = 0; cur_folio < nr_folios; ++cur_folio) {
> @@ -391,14 +383,15 @@ static long udmabuf_pin_folios(struct udmabuf
> *ubuf, struct file *memfd,
> end:
> ubuf->pagecount = upgcnt;
> ubuf->nr_pinned = nr_pinned;
> - kvfree(folios);
> - return ret;
> + return 0;
> }
>
> static long udmabuf_create(struct miscdevice *device,
> struct udmabuf_create_list *head,
> struct udmabuf_create_item *list)
> {
> + unsigned long max_nr_folios = 0;
> + struct folio **folios = NULL;
> pgoff_t pgcnt = 0, pglimit;
> struct udmabuf *ubuf;
> long ret = -EINVAL;
> @@ -410,14 +403,19 @@ static long udmabuf_create(struct miscdevice
> *device,
>
> pglimit = (size_limit_mb * 1024 * 1024) >> PAGE_SHIFT;
> for (i = 0; i < head->count; i++) {
> + pgoff_t subpgcnt;
> +
> if (!PAGE_ALIGNED(list[i].offset))
> goto err_noinit;
> if (!PAGE_ALIGNED(list[i].size))
> goto err_noinit;
>
> - pgcnt += list[i].size >> PAGE_SHIFT;
> + subpgcnt = list[i].size >> PAGE_SHIFT;
> + pgcnt += subpgcnt;
> if (pgcnt > pglimit)
> goto err_noinit;
> +
> + max_nr_folios = max_t(unsigned long, subpgcnt,
> max_nr_folios);
> }
>
> if (!pgcnt)
> @@ -427,6 +425,12 @@ static long udmabuf_create(struct miscdevice
> *device,
> if (ret)
> goto err;
>
> + folios = kvmalloc_array(max_nr_folios, sizeof(*folios), GFP_KERNEL);
> + if (!folios) {
> + ret = -ENOMEM;
> + goto err;
> + }
> +
> for (i = 0; i < head->count; i++) {
> struct file *memfd = fget(list[i].memfd);
>
> @@ -442,7 +446,7 @@ static long udmabuf_create(struct miscdevice
> *device,
> }
>
> ret = udmabuf_pin_folios(ubuf, memfd, list[i].offset,
> - list[i].size);
> + list[i].size, folios);
> fput(memfd);
> if (ret)
> goto err;
> @@ -453,12 +457,14 @@ static long udmabuf_create(struct miscdevice
> *device,
> if (ret < 0)
> goto err;
>
> + kvfree(folios);
> return ret;
>
> err:
> deinit_udmabuf(ubuf);
> err_noinit:
> kfree(ubuf);
> + kvfree(folios);
> return ret;
> }
>
> --
> 2.45.2
