Hi Shakeel,
On Fri, Dec 28, 2018 at 05:31:47PM -0800, Shakeel Butt wrote:
> __alloc_percpu_gfp() can be called from atomic context, so, make
> pcpu_get_pages use the gfp provided to the higher layer.
>
> Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> ---
> mm/percpu-vm.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
> index d8078de912de..4f42c4c5c902 100644
> --- a/mm/percpu-vm.c
> +++ b/mm/percpu-vm.c
> @@ -21,6 +21,7 @@ static struct page *pcpu_chunk_page(struct pcpu_chunk *chunk,
>
> /**
> * pcpu_get_pages - get temp pages array
> + * @gfp: allocation flags passed to the underlying allocator
> *
> * Returns pointer to array of pointers to struct page which can be indexed
> * with pcpu_page_idx(). Note that there is only one array and accesses
> @@ -29,7 +30,7 @@ static struct page *pcpu_chunk_page(struct pcpu_chunk *chunk,
> * RETURNS:
> * Pointer to temp pages array on success.
> */
> -static struct page **pcpu_get_pages(void)
> +static struct page **pcpu_get_pages(gfp_t gfp)
> {
> static struct page **pages;
> size_t pages_size = pcpu_nr_units * pcpu_unit_pages * sizeof(pages[0]);
> @@ -37,7 +38,7 @@ static struct page **pcpu_get_pages(void)
> lockdep_assert_held(&pcpu_alloc_mutex);
>
> if (!pages)
> - pages = pcpu_mem_zalloc(pages_size, GFP_KERNEL);
> + pages = pcpu_mem_zalloc(pages_size, gfp);
> return pages;
> }
>
> @@ -278,7 +279,7 @@ static int pcpu_populate_chunk(struct pcpu_chunk *chunk,
> {
> struct page **pages;
>
> - pages = pcpu_get_pages();
> + pages = pcpu_get_pages(gfp);
> if (!pages)
> return -ENOMEM;
>
> @@ -316,7 +317,7 @@ static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
> * successful population attempt so the temp pages array must
> * be available now.
> */
> - pages = pcpu_get_pages();
> + pages = pcpu_get_pages(GFP_KERNEL);
> BUG_ON(!pages);
>
> /* unmap and free */
> --
> 2.20.1.415.g653613c723-goog
>
Sorry, I'm travelling today and was hoping to respond to this later
tonight.
So percpu memory is a little different as it's an intermediary. When you
call __alloc_percpu_gfp() and it does not contain GFP_KERNEL, it is
considered atomic. So, we only service requests out of already
populated memory. pcpu_get_pages() is only called when we need to
populate/depopulate a chunk and will not be called if we need an atomic
allocation. Also, in all but the first case, it won't make an allocation
as pages is a static variable.
Furthermore, percpu only plumbs through certain gfp as not all make
sense [1].
[1] https://lore.kernel.org/lkml/cover.1518668149.git.dennisszhou@xxxxxxxxx/
Thanks,
Dennis
