Re: [PATCH v5 7/7] udmabuf: reuse folio array when pin folios

[Huan Yang <link@xxxxxxxx>]

在 2024/9/6 16:23, Kasireddy, Vivek 写道:
> Hi Huan,
>
> > Subject: [PATCH v5 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
> > 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.
> >
> > But if size is huge, need fallback into vmalloc, then, not well, due to
> > each page will iter alloc, and map into vmalloc area. Too heavy.
> >
> > 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>
> > ---
> >   drivers/dma-buf/udmabuf.c | 34 ++++++++++++++++++++--------------
> >   1 file changed, 20 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> > index d449c1fd67a5..d70e45c33442 100644
> > --- a/drivers/dma-buf/udmabuf.c
> > +++ b/drivers/dma-buf/udmabuf.c
> > @@ -343,28 +343,21 @@ static int export_udmabuf(struct udmabuf *ubuf,
> >   }
> >
> >   static int 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 pgoff, pgcnt;
> >   	pgoff_t upgcnt = ubuf->pagecount;
> >   	pgoff_t nr_pinned = ubuf->nr_pinned;
> >   	u32 cur_folio, cur_pgcnt;
> > -	struct folio **folios = NULL;
> >   	long nr_folios;
> >   	loff_t end;
> >   	int ret = 0;
> >
> >   	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 err;
> > -	}
> > +	if (nr_folios <= 0)
> > +		return nr_folios ? nr_folios : -EINVAL;
> >
> >   	cur_pgcnt = 0;
> >   	for (cur_folio = 0; cur_folio < nr_folios; ++cur_folio) {
> > @@ -389,10 +382,8 @@ static int udmabuf_pin_folios(struct udmabuf
> > *ubuf, struct file *memfd,
> >   		pgoff = 0;
> >   	}
> >   end:
> > -err:
> >   	ubuf->pagecount = upgcnt;
> >   	ubuf->nr_pinned = nr_pinned;
> > -	kvfree(folios);
> >   	return ret;
> The variable ret is now unused in this function. Remove it and just
> return 0 at the end.

Oh, nice catch.

Thanks.

> >   }
> >
> > @@ -403,6 +394,8 @@ static long udmabuf_create(struct miscdevice
> > *device,
> >   	pgoff_t pgcnt = 0, pglimit;
> >   	long ret = -EINVAL;
> >   	struct udmabuf *ubuf;
> > +	struct folio **folios = NULL;
> > +	unsigned long max_nr_folios = 0;
> >   	u32 i, flags;
> >
> >   	ubuf = kzalloc(sizeof(*ubuf), GFP_KERNEL);
> > @@ -411,14 +404,19 @@ 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)
> > @@ -428,6 +426,12 @@ 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);
> >
> > @@ -436,7 +440,7 @@ static long udmabuf_create(struct miscdevice
> > *device,
> >   			goto err;
> >
> >   		ret = udmabuf_pin_folios(ubuf, memfd, list[i].offset,
> > -					 list[i].size);
> > +					 list[i].size, folios);
> >   		fput(memfd);
> >   		if (ret)
> >   			goto err;
> > @@ -447,12 +451,14 @@ static long udmabuf_create(struct miscdevice
> > *device,
> >   	if (ret < 0)
> >   		goto err;
> >
> > +	kvfree(folios);
> Acked-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
>
> >   	return ret;
> >
> >   err:
> >   	deinit_udmabuf(ubuf);
> >   err_noinit:
> >   	kfree(ubuf);
> > +	kvfree(folios);
> >   	return ret;
> >   }
> >
> > --
> > 2.45.2