On Tue, Oct 14, 2025 at 7:59 PM Christian König
<[email protected]> wrote:
>
> On 14.10.25 10:32, zhaoyang.huang wrote:
> > From: Zhaoyang Huang <[email protected]>
> >
> > The size of once dma-buf allocation could be dozens MB or much more
> > which introduce a loop of allocating several thousands of order-0 pages.
> > Furthermore, the concurrent allocation could have dma-buf allocation enter
> > direct-reclaim during the loop. This commit would like to eliminate the
> > above two affections by introducing alloc_pages_bulk_list in dma-buf's
> > order-0 allocation. This patch is proved to be conditionally helpful
> > in 18MB allocation as decreasing the time from 24604us to 6555us and no
> > harm when bulk allocation can't be done(fallback to single page
> > allocation)
>
> Well that sounds like an absolutely horrible idea.
>
> See the handling of allocating only from specific order is *exactly* there to
> avoid the behavior of bulk allocation.
>
> What you seem to do with this patch here is to add on top of the behavior to
> avoid allocating large chunks from the buddy the behavior to allocate large
> chunks from the buddy because that is faster.
emm, this patch doesn't change order-8 and order-4's allocation
behaviour but just to replace the loop of order-0 allocations into
once bulk allocation in the fallback way. What is your concern about
this?
>
> So this change here doesn't looks like it will fly very high. Please explain
> what you're actually trying to do, just optimize allocation time?
>
> Regards,
> Christian.
>
> > Signed-off-by: Zhaoyang Huang <[email protected]>
> > ---
> > drivers/dma-buf/heaps/system_heap.c | 36 +++++++++++++++++++----------
> > 1 file changed, 24 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/dma-buf/heaps/system_heap.c
> > b/drivers/dma-buf/heaps/system_heap.c
> > index bbe7881f1360..71b028c63bd8 100644
> > --- a/drivers/dma-buf/heaps/system_heap.c
> > +++ b/drivers/dma-buf/heaps/system_heap.c
> > @@ -300,8 +300,8 @@ static const struct dma_buf_ops system_heap_buf_ops = {
> > .release = system_heap_dma_buf_release,
> > };
> >
> > -static struct page *alloc_largest_available(unsigned long size,
> > - unsigned int max_order)
> > +static void alloc_largest_available(unsigned long size,
> > + unsigned int max_order, unsigned int *num_pages, struct
> > list_head *list)
> > {
> > struct page *page;
> > int i;
> > @@ -312,12 +312,19 @@ static struct page *alloc_largest_available(unsigned
> > long size,
> > if (max_order < orders[i])
> > continue;
> >
> > - page = alloc_pages(order_flags[i], orders[i]);
> > - if (!page)
> > + if (orders[i]) {
> > + page = alloc_pages(order_flags[i], orders[i]);
> > + if (page) {
> > + list_add(&page->lru, list);
> > + *num_pages = 1;
> > + }
> > + } else
> > + *num_pages = alloc_pages_bulk_list(LOW_ORDER_GFP,
> > size / PAGE_SIZE, list);
> > +
> > + if (list_empty(list))
> > continue;
> > - return page;
> > + return;
> > }
> > - return NULL;
> > }
> >
> > static struct dma_buf *system_heap_allocate(struct dma_heap *heap,
> > @@ -335,6 +342,8 @@ static struct dma_buf *system_heap_allocate(struct
> > dma_heap *heap,
> > struct list_head pages;
> > struct page *page, *tmp_page;
> > int i, ret = -ENOMEM;
> > + unsigned int num_pages;
> > + LIST_HEAD(head);
> >
> > buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
> > if (!buffer)
> > @@ -348,6 +357,8 @@ static struct dma_buf *system_heap_allocate(struct
> > dma_heap *heap,
> > INIT_LIST_HEAD(&pages);
> > i = 0;
> > while (size_remaining > 0) {
> > + num_pages = 0;
> > + INIT_LIST_HEAD(&head);
> > /*
> > * Avoid trying to allocate memory if the process
> > * has been killed by SIGKILL
> > @@ -357,14 +368,15 @@ static struct dma_buf *system_heap_allocate(struct
> > dma_heap *heap,
> > goto free_buffer;
> > }
> >
> > - page = alloc_largest_available(size_remaining, max_order);
> > - if (!page)
> > + alloc_largest_available(size_remaining, max_order,
> > &num_pages, &head);
> > + if (!num_pages)
> > goto free_buffer;
> >
> > - list_add_tail(&page->lru, &pages);
> > - size_remaining -= page_size(page);
> > - max_order = compound_order(page);
> > - i++;
> > + list_splice_tail(&head, &pages);
> > + max_order = folio_order(lru_to_folio(&head));
> > + size_remaining -= PAGE_SIZE * (num_pages << max_order);
> > + i += num_pages;
> > +
> > }
> >
> > table = &buffer->sg_table;
>
