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SubjectRe: [PATCH] adjust gfp mask passed on nested vmalloc() invocation
On Mon, 5 Oct 2009, Jan Beulich wrote:

> - fix a latent bug resulting from blindly or-ing in __GFP_ZERO, since
> the combination of this and __GFP_HIGHMEM (possibly passed into the
> function) is forbidden in interrupt context
> - avoid wasting more precious resources (DMA or DMA32 pools), when
> being called through vmalloc_32{,_user}()
> - explicitly allow using high memory here even if the outer allocation
> request doesn't allow it, unless is collides with __GFP_ZERO
>
> Signed-off-by: Jan Beulich <jbeulich@novell.com>

I thought vmalloc.c was a BUG_ON(in_interrupt()) zone?
The locking is all spin_lock stuff, not spin_lock_irq stuff.
That's probably why your "bug" has remained "latent".

Using HIGHMEM for internal arrays looks reasonable to me; but if
__GFP_ZERO were a problem, wouldn't it be much cleaner to skip the
"unless it collides" and #ifdef CONFIG_HIGHMEM !in_interrupt() stuff,
just memset the array returned from __vmalloc_node()?

Hugh

>
> ---
> mm/vmalloc.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> --- linux-2.6.32-rc3/mm/vmalloc.c 2009-10-05 11:59:56.000000000 +0200
> +++ 2.6.32-rc3-vmalloc-nested-gfp/mm/vmalloc.c 2009-10-05 08:40:36.000000000 +0200
> @@ -1410,6 +1410,7 @@ static void *__vmalloc_area_node(struct
> {
> struct page **pages;
> unsigned int nr_pages, array_size, i;
> + gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO;
>
> nr_pages = (area->size - PAGE_SIZE) >> PAGE_SHIFT;
> array_size = (nr_pages * sizeof(struct page *));
> @@ -1417,13 +1418,16 @@ static void *__vmalloc_area_node(struct
> area->nr_pages = nr_pages;
> /* Please note that the recursion is strictly bounded. */
> if (array_size > PAGE_SIZE) {
> - pages = __vmalloc_node(array_size, gfp_mask | __GFP_ZERO,
> +#ifdef CONFIG_HIGHMEM
> + /* See the comment in prep_zero_page(). */
> + if (!in_interrupt())
> + nested_gfp |= __GFP_HIGHMEM;
> +#endif
> + pages = __vmalloc_node(array_size, nested_gfp,
> PAGE_KERNEL, node, caller);
> area->flags |= VM_VPAGES;
> } else {
> - pages = kmalloc_node(array_size,
> - (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO,
> - node);
> + pages = kmalloc_node(array_size, nested_gfp, node);
> }
> area->pages = pages;
> area->caller = caller;


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