Re: [PATCH 1/8] btrfs: bioset allocations will never fail, adapt our helpers

[Anand Jain]

Reviewed-by: Anand Jain 
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Re: [PATCH 1/8] btrfs: bioset allocations will never fail, adapt our helpers

[Anand Jain]

#define __GFP_RECLAIM ((__force 
gfp_t)(___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM))


#define GFP_NOFS(__GFP_RECLAIM | __GFP_IO)


  Ah. Thanks.
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Re: [PATCH 1/8] btrfs: bioset allocations will never fail, adapt our helpers

[David Sterba]

On Tue, Jun 06, 2017 at 06:21:17PM +0800, Anand Jain wrote:
> On 06/03/17 00:58, David Sterba wrote:
> > Christoph pointed out that bio allocations backed by a bioset will never
> > fail.
> 
>   Looks like this feature comes when  __GFP_DIRECT_RECLAIM is
>   set and we aren't, such as [1]. Any idea why? Looks like I am
>   missing something ?

bio_alloc_bioset:

 406  *   When @bs is not NULL, if %__GFP_DIRECT_RECLAIM is set then bio_alloc 
will
 407  *   always be able to allocate a bio. This is due to the mempool 
guarantees.

> [1]
> -
> static int submit_extent_page(int op, int op_flags, struct 
> extent_io_tree *tree,
> ::
> 
>   bio = btrfs_bio_alloc(bdev, sector, BIO_MAX_PAGES,
>  GFP_NOFS | __GFP_HIGH);

GFP_NOFS contains __GFP_DIRECT_RECLAIM, so what's the problem? __GFP_HIGH
allows using the reserves, but should not otherwise change the constraints.
And it's use seems unnecessary, as far as I could track in the history.
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Re: [PATCH 1/8] btrfs: bioset allocations will never fail, adapt our helpers

[Christoph Hellwig]

On Tue, Jun 06, 2017 at 06:21:17PM +0800, Anand Jain wrote:
>
>
> On 06/03/17 00:58, David Sterba wrote:
>> Christoph pointed out that bio allocations backed by a bioset will never
>> fail.
>
> David,
>
>  Looks like this feature comes when  __GFP_DIRECT_RECLAIM is
>  set and we aren't, such as [1]. Any idea why? Looks like I am
>  missing something ?
>
>
> [1]
> -
> static int submit_extent_page(int op, int op_flags, struct extent_io_tree 
> *tree,
> ::
>
>  bio = btrfs_bio_alloc(bdev, sector, BIO_MAX_PAGES,
> GFP_NOFS | __GFP_HIGH);

#define __GFP_RECLAIM ((__force 
gfp_t)(___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM))


#define GFP_NOFS(__GFP_RECLAIM | __GFP_IO)

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Re: [PATCH 1/8] btrfs: bioset allocations will never fail, adapt our helpers

[Anand Jain]

On 06/03/17 00:58, David Sterba wrote:

Christoph pointed out that bio allocations backed by a bioset will never
fail.


David,

 Looks like this feature comes when  __GFP_DIRECT_RECLAIM is
 set and we aren't, such as [1]. Any idea why? Looks like I am
 missing something ?


[1]
-
static int submit_extent_page(int op, int op_flags, struct 
extent_io_tree *tree,

::

 bio = btrfs_bio_alloc(bdev, sector, BIO_MAX_PAGES,
GFP_NOFS | __GFP_HIGH);

--

Thanks, Anand



 As we always use a bioset for all bio allocations, we can skip
the error handling.  This patch adjusts our low-level helpers, the
cascaded changes to all callers will come next.

CC: Christoph Hellwig 
CC: Liu Bo 
Signed-off-by: David Sterba 
---
 fs/btrfs/extent_io.c | 50 +++---
 1 file changed, 19 insertions(+), 31 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 5909f8214255..78a787c36a35 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2659,8 +2659,9 @@ static void end_bio_extent_readpage(struct bio *bio)
 }

 /*
- * this allocates from the btrfs_bioset.  We're returning a bio right now
- * but you can call btrfs_io_bio for the appropriate container_of magic
+ * The following helpers allocate a bio. As it's backed by a bioset, it'll
+ * never fail.  We're returning a bio right now but you can call btrfs_io_bio
+ * for the appropriate container_of magic
  */
 struct bio *
 btrfs_bio_alloc(struct block_device *bdev, u64 first_sector, int nr_vecs,
@@ -2670,22 +2671,12 @@ btrfs_bio_alloc(struct block_device *bdev, u64 
first_sector, int nr_vecs,
struct bio *bio;

bio = bio_alloc_bioset(gfp_flags, nr_vecs, btrfs_bioset);
-
-   if (bio == NULL && (current->flags & PF_MEMALLOC)) {
-   while (!bio && (nr_vecs /= 2)) {
-   bio = bio_alloc_bioset(gfp_flags,
-  nr_vecs, btrfs_bioset);
-   }
-   }
-
-   if (bio) {
-   bio->bi_bdev = bdev;
-   bio->bi_iter.bi_sector = first_sector;
-   btrfs_bio = btrfs_io_bio(bio);
-   btrfs_bio->csum = NULL;
-   btrfs_bio->csum_allocated = NULL;
-   btrfs_bio->end_io = NULL;
-   }
+   bio->bi_bdev = bdev;
+   bio->bi_iter.bi_sector = first_sector;
+   btrfs_bio = btrfs_io_bio(bio);
+   btrfs_bio->csum = NULL;
+   btrfs_bio->csum_allocated = NULL;
+   btrfs_bio->end_io = NULL;
return bio;
 }

@@ -2694,29 +2685,26 @@ struct bio *btrfs_bio_clone(struct bio *bio, gfp_t 
gfp_mask)
struct btrfs_io_bio *btrfs_bio;
struct bio *new;

+   /* Bio allocation backed by a bioset does not fail */
new = bio_clone_fast(bio, gfp_mask, btrfs_bioset);
-   if (new) {
-   btrfs_bio = btrfs_io_bio(new);
-   btrfs_bio->csum = NULL;
-   btrfs_bio->csum_allocated = NULL;
-   btrfs_bio->end_io = NULL;
-   }
+   btrfs_bio = btrfs_io_bio(new);
+   btrfs_bio->csum = NULL;
+   btrfs_bio->csum_allocated = NULL;
+   btrfs_bio->end_io = NULL;
return new;
 }

-/* this also allocates from the btrfs_bioset */
 struct bio *btrfs_io_bio_alloc(gfp_t gfp_mask, unsigned int nr_iovecs)
 {
struct btrfs_io_bio *btrfs_bio;
struct bio *bio;

+   /* Bio allocation backed by a bioset does not fail */
bio = bio_alloc_bioset(gfp_mask, nr_iovecs, btrfs_bioset);
-   if (bio) {
-   btrfs_bio = btrfs_io_bio(bio);
-   btrfs_bio->csum = NULL;
-   btrfs_bio->csum_allocated = NULL;
-   btrfs_bio->end_io = NULL;
-   }
+   btrfs_bio = btrfs_io_bio(bio);
+   btrfs_bio->csum = NULL;
+   btrfs_bio->csum_allocated = NULL;
+   btrfs_bio->end_io = NULL;
return bio;
 }



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Re: [PATCH 1/8] btrfs: bioset allocations will never fail, adapt our helpers

[Christoph Hellwig]

On Fri, Jun 02, 2017 at 06:58:30PM +0200, David Sterba wrote:
> Christoph pointed out that bio allocations backed by a bioset will never
> fail.  As we always use a bioset for all bio allocations, we can skip
> the error handling.  This patch adjusts our low-level helpers, the
> cascaded changes to all callers will come next.

Looks good,

Reviewed-by: Christoph Hellwig 
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[PATCH 1/8] btrfs: bioset allocations will never fail, adapt our helpers

[David Sterba]

Christoph pointed out that bio allocations backed by a bioset will never
fail.  As we always use a bioset for all bio allocations, we can skip
the error handling.  This patch adjusts our low-level helpers, the
cascaded changes to all callers will come next.

CC: Christoph Hellwig 
CC: Liu Bo 
Signed-off-by: David Sterba 
---
 fs/btrfs/extent_io.c | 50 +++---
 1 file changed, 19 insertions(+), 31 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 5909f8214255..78a787c36a35 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2659,8 +2659,9 @@ static void end_bio_extent_readpage(struct bio *bio)
 }
 
 /*
- * this allocates from the btrfs_bioset.  We're returning a bio right now
- * but you can call btrfs_io_bio for the appropriate container_of magic
+ * The following helpers allocate a bio. As it's backed by a bioset, it'll
+ * never fail.  We're returning a bio right now but you can call btrfs_io_bio
+ * for the appropriate container_of magic
  */
 struct bio *
 btrfs_bio_alloc(struct block_device *bdev, u64 first_sector, int nr_vecs,
@@ -2670,22 +2671,12 @@ btrfs_bio_alloc(struct block_device *bdev, u64 
first_sector, int nr_vecs,
struct bio *bio;
 
bio = bio_alloc_bioset(gfp_flags, nr_vecs, btrfs_bioset);
-
-   if (bio == NULL && (current->flags & PF_MEMALLOC)) {
-   while (!bio && (nr_vecs /= 2)) {
-   bio = bio_alloc_bioset(gfp_flags,
-  nr_vecs, btrfs_bioset);
-   }
-   }
-
-   if (bio) {
-   bio->bi_bdev = bdev;
-   bio->bi_iter.bi_sector = first_sector;
-   btrfs_bio = btrfs_io_bio(bio);
-   btrfs_bio->csum = NULL;
-   btrfs_bio->csum_allocated = NULL;
-   btrfs_bio->end_io = NULL;
-   }
+   bio->bi_bdev = bdev;
+   bio->bi_iter.bi_sector = first_sector;
+   btrfs_bio = btrfs_io_bio(bio);
+   btrfs_bio->csum = NULL;
+   btrfs_bio->csum_allocated = NULL;
+   btrfs_bio->end_io = NULL;
return bio;
 }
 
@@ -2694,29 +2685,26 @@ struct bio *btrfs_bio_clone(struct bio *bio, gfp_t 
gfp_mask)
struct btrfs_io_bio *btrfs_bio;
struct bio *new;
 
+   /* Bio allocation backed by a bioset does not fail */
new = bio_clone_fast(bio, gfp_mask, btrfs_bioset);
-   if (new) {
-   btrfs_bio = btrfs_io_bio(new);
-   btrfs_bio->csum = NULL;
-   btrfs_bio->csum_allocated = NULL;
-   btrfs_bio->end_io = NULL;
-   }
+   btrfs_bio = btrfs_io_bio(new);
+   btrfs_bio->csum = NULL;
+   btrfs_bio->csum_allocated = NULL;
+   btrfs_bio->end_io = NULL;
return new;
 }
 
-/* this also allocates from the btrfs_bioset */
 struct bio *btrfs_io_bio_alloc(gfp_t gfp_mask, unsigned int nr_iovecs)
 {
struct btrfs_io_bio *btrfs_bio;
struct bio *bio;
 
+   /* Bio allocation backed by a bioset does not fail */
bio = bio_alloc_bioset(gfp_mask, nr_iovecs, btrfs_bioset);
-   if (bio) {
-   btrfs_bio = btrfs_io_bio(bio);
-   btrfs_bio->csum = NULL;
-   btrfs_bio->csum_allocated = NULL;
-   btrfs_bio->end_io = NULL;
-   }
+   btrfs_bio = btrfs_io_bio(bio);
+   btrfs_bio->csum = NULL;
+   btrfs_bio->csum_allocated = NULL;
+   btrfs_bio->end_io = NULL;
return bio;
 }
 
-- 
2.12.0

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