On 01/06/2017 03:11 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> kmem_zalloc_large and _xfs_buf_map_pages use memalloc_noio_{save,restore}
> API to prevent from reclaim recursion into the fs because vmalloc can
> invoke unconditional GFP_KERNEL allocations and these functions might be
> called from the NOFS contexts. The memalloc_noio_save will enforce
> GFP_NOIO context which is even weaker than GFP_NOFS and that seems to be
> unnecessary. Let's use memalloc_nofs_{save,restore} instead as it should
> provide exactly what we need here - implicit GFP_NOFS context.
>
> Changes since v1
> - s@memalloc_noio_restore@memalloc_nofs_restore@ in _xfs_buf_map_pages
> as per Brian Foster
>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Not a xfs expert, but seems correct.
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Nit below:
> ---
> fs/xfs/kmem.c | 10 +++++-----
> fs/xfs/xfs_buf.c | 8 ++++----
> 2 files changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> index a76a05dae96b..d69ed5e76621 100644
> --- a/fs/xfs/kmem.c
> +++ b/fs/xfs/kmem.c
> @@ -65,7 +65,7 @@ kmem_alloc(size_t size, xfs_km_flags_t flags)
> void *
> kmem_zalloc_large(size_t size, xfs_km_flags_t flags)
> {
> - unsigned noio_flag = 0;
> + unsigned nofs_flag = 0;
> void *ptr;
> gfp_t lflags;
>
> @@ -80,14 +80,14 @@ kmem_zalloc_large(size_t size, xfs_km_flags_t flags)
> * context via PF_MEMALLOC_NOIO to prevent memory reclaim re-entering
> * the filesystem here and potentially deadlocking.
The comment above is now largely obsolete, or minimally should be
changed to PF_MEMALLOC_NOFS?
> */
> - if ((current->flags & PF_MEMALLOC_NOFS) || (flags & KM_NOFS))
> - noio_flag = memalloc_noio_save();
> + if (flags & KM_NOFS)
> + nofs_flag = memalloc_nofs_save();
>
> lflags = kmem_flags_convert(flags);
> ptr = __vmalloc(size, lflags | __GFP_HIGHMEM | __GFP_ZERO, PAGE_KERNEL);
>
> - if ((current->flags & PF_MEMALLOC_NOFS) || (flags & KM_NOFS))
> - memalloc_noio_restore(noio_flag);
> + if (flags & KM_NOFS)
> + memalloc_nofs_restore(nofs_flag);
>
> return ptr;
> }
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 7f0a01f7b592..8cb8dd4cdfd8 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -441,17 +441,17 @@ _xfs_buf_map_pages(
> bp->b_addr = NULL;
> } else {
> int retried = 0;
> - unsigned noio_flag;
> + unsigned nofs_flag;
>
> /*
> * vm_map_ram() will allocate auxillary structures (e.g.
> * pagetables) with GFP_KERNEL, yet we are likely to be under
> * GFP_NOFS context here. Hence we need to tell memory reclaim
> - * that we are in such a context via PF_MEMALLOC_NOIO to prevent
> + * that we are in such a context via PF_MEMALLOC_NOFS to prevent
> * memory reclaim re-entering the filesystem here and
> * potentially deadlocking.
> */
> - noio_flag = memalloc_noio_save();
> + nofs_flag = memalloc_nofs_save();
> do {
> bp->b_addr = vm_map_ram(bp->b_pages, bp->b_page_count,
> -1, PAGE_KERNEL);
> @@ -459,7 +459,7 @@ _xfs_buf_map_pages(
> break;
> vm_unmap_aliases();
> } while (retried++ <= 1);
> - memalloc_noio_restore(noio_flag);
> + memalloc_nofs_restore(nofs_flag);
>
> if (!bp->b_addr)
> return -ENOMEM;
>
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