* [PATCH] mm: bio_alloc never fails when set GFP_NOIO, GFP_KERNEL
@ 2020-10-21 3:11 Xianting Tian
2020-10-23 16:40 ` Tianxianting
2020-10-25 19:09 ` Andrew Morton
0 siblings, 2 replies; 4+ messages in thread
From: Xianting Tian @ 2020-10-21 3:11 UTC (permalink / raw)
To: akpm; +Cc: linux-mm, linux-kernel, Xianting Tian
bio_alloc with __GFP_DIRECT_RECLAIM(which is included in GFP_NOIO,
GFP_KERNEL) never fails, as stated in the comments of bio_alloc_bioset.
So we can remove multiple unneeded null checks of bio_alloc and simplify
the code.
We have done it in fs/ext4/readpage.c, fs/ext4/page-io.c, fs/direct-io.c,
and so forth.
Signed-off-by: Xianting Tian <tian.xianting@h3c.com>
---
mm/page_io.c | 31 +++++++++++--------------------
1 file changed, 11 insertions(+), 20 deletions(-)
diff --git a/mm/page_io.c b/mm/page_io.c
index e485a6e8a..9215bb356 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -30,18 +30,20 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
struct page *page, bio_end_io_t end_io)
{
struct bio *bio;
+ struct block_device *bdev;
+ /*
+ * bio_alloc will _always_ be able to allocate a bio if
+ * __GFP_DIRECT_RECLAIM is set, see comments for bio_alloc_bioset().
+ */
bio = bio_alloc(gfp_flags, 1);
- if (bio) {
- struct block_device *bdev;
+ bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
+ bio_set_dev(bio, bdev);
+ bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
+ bio->bi_end_io = end_io;
- bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
- bio_set_dev(bio, bdev);
- bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
- bio->bi_end_io = end_io;
+ bio_add_page(bio, page, thp_size(page), 0);
- bio_add_page(bio, page, thp_size(page), 0);
- }
return bio;
}
@@ -351,19 +353,13 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
ret = 0;
bio = get_swap_bio(GFP_NOIO, page, end_write_func);
- if (bio == NULL) {
- set_page_dirty(page);
- unlock_page(page);
- ret = -ENOMEM;
- goto out;
- }
bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
bio_associate_blkg_from_page(bio, page);
count_swpout_vm_event(page);
set_page_writeback(page);
unlock_page(page);
submit_bio(bio);
-out:
+
return ret;
}
@@ -416,11 +412,6 @@ int swap_readpage(struct page *page, bool synchronous)
ret = 0;
bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
- if (bio == NULL) {
- unlock_page(page);
- ret = -ENOMEM;
- goto out;
- }
disk = bio->bi_disk;
/*
* Keep this task valid during swap readpage because the oom killer may
--
2.17.1
^ permalink raw reply related [flat|nested] 4+ messages in thread* RE: [PATCH] mm: bio_alloc never fails when set GFP_NOIO, GFP_KERNEL
2020-10-21 3:11 [PATCH] mm: bio_alloc never fails when set GFP_NOIO, GFP_KERNEL Xianting Tian
@ 2020-10-23 16:40 ` Tianxianting
2020-10-25 19:09 ` Andrew Morton
1 sibling, 0 replies; 4+ messages in thread
From: Tianxianting @ 2020-10-23 16:40 UTC (permalink / raw)
To: akpm; +Cc: linux-mm, linux-kernel
Hi Andrew
Could I get your comments for this patch? Thanks in advance.
-----Original Message-----
From: tianxianting (RD)
Sent: Wednesday, October 21, 2020 11:11 AM
To: akpm@linux-foundation.org
Cc: linux-mm@kvack.org; linux-kernel@vger.kernel.org; tianxianting (RD) <tian.xianting@h3c.com>
Subject: [PATCH] mm: bio_alloc never fails when set GFP_NOIO, GFP_KERNEL
bio_alloc with __GFP_DIRECT_RECLAIM(which is included in GFP_NOIO,
GFP_KERNEL) never fails, as stated in the comments of bio_alloc_bioset.
So we can remove multiple unneeded null checks of bio_alloc and simplify the code.
We have done it in fs/ext4/readpage.c, fs/ext4/page-io.c, fs/direct-io.c, and so forth.
Signed-off-by: Xianting Tian <tian.xianting@h3c.com>
---
mm/page_io.c | 31 +++++++++++--------------------
1 file changed, 11 insertions(+), 20 deletions(-)
diff --git a/mm/page_io.c b/mm/page_io.c index e485a6e8a..9215bb356 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -30,18 +30,20 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
struct page *page, bio_end_io_t end_io) {
struct bio *bio;
+ struct block_device *bdev;
+ /*
+ * bio_alloc will _always_ be able to allocate a bio if
+ * __GFP_DIRECT_RECLAIM is set, see comments for bio_alloc_bioset().
+ */
bio = bio_alloc(gfp_flags, 1);
- if (bio) {
- struct block_device *bdev;
+ bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
+ bio_set_dev(bio, bdev);
+ bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
+ bio->bi_end_io = end_io;
- bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
- bio_set_dev(bio, bdev);
- bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
- bio->bi_end_io = end_io;
+ bio_add_page(bio, page, thp_size(page), 0);
- bio_add_page(bio, page, thp_size(page), 0);
- }
return bio;
}
@@ -351,19 +353,13 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
ret = 0;
bio = get_swap_bio(GFP_NOIO, page, end_write_func);
- if (bio == NULL) {
- set_page_dirty(page);
- unlock_page(page);
- ret = -ENOMEM;
- goto out;
- }
bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
bio_associate_blkg_from_page(bio, page);
count_swpout_vm_event(page);
set_page_writeback(page);
unlock_page(page);
submit_bio(bio);
-out:
+
return ret;
}
@@ -416,11 +412,6 @@ int swap_readpage(struct page *page, bool synchronous)
ret = 0;
bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
- if (bio == NULL) {
- unlock_page(page);
- ret = -ENOMEM;
- goto out;
- }
disk = bio->bi_disk;
/*
* Keep this task valid during swap readpage because the oom killer may
--
2.17.1
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] mm: bio_alloc never fails when set GFP_NOIO, GFP_KERNEL
2020-10-21 3:11 [PATCH] mm: bio_alloc never fails when set GFP_NOIO, GFP_KERNEL Xianting Tian
2020-10-23 16:40 ` Tianxianting
@ 2020-10-25 19:09 ` Andrew Morton
2020-10-25 19:24 ` Jens Axboe
1 sibling, 1 reply; 4+ messages in thread
From: Andrew Morton @ 2020-10-25 19:09 UTC (permalink / raw)
To: Xianting Tian; +Cc: linux-mm, linux-kernel, Jens Axboe
On Wed, 21 Oct 2020 11:11:28 +0800 Xianting Tian <tian.xianting@h3c.com> wrote:
> bio_alloc with __GFP_DIRECT_RECLAIM(which is included in GFP_NOIO,
> GFP_KERNEL) never fails, as stated in the comments of bio_alloc_bioset.
>
> So we can remove multiple unneeded null checks of bio_alloc and simplify
> the code.
>
> We have done it in fs/ext4/readpage.c, fs/ext4/page-io.c, fs/direct-io.c,
> and so forth.
>
(cc Jens)
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -30,18 +30,20 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
> struct page *page, bio_end_io_t end_io)
> {
> struct bio *bio;
> + struct block_device *bdev;
>
> + /*
> + * bio_alloc will _always_ be able to allocate a bio if
> + * __GFP_DIRECT_RECLAIM is set, see comments for bio_alloc_bioset().
> + */
> bio = bio_alloc(gfp_flags, 1);
> - if (bio) {
> - struct block_device *bdev;
> + bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
> + bio_set_dev(bio, bdev);
> + bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
> + bio->bi_end_io = end_io;
>
> - bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
> - bio_set_dev(bio, bdev);
> - bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
> - bio->bi_end_io = end_io;
> + bio_add_page(bio, page, thp_size(page), 0);
>
> - bio_add_page(bio, page, thp_size(page), 0);
> - }
> return bio;
> }
>
> @@ -351,19 +353,13 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
>
> ret = 0;
> bio = get_swap_bio(GFP_NOIO, page, end_write_func);
> - if (bio == NULL) {
> - set_page_dirty(page);
> - unlock_page(page);
> - ret = -ENOMEM;
> - goto out;
> - }
> bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
> bio_associate_blkg_from_page(bio, page);
> count_swpout_vm_event(page);
> set_page_writeback(page);
> unlock_page(page);
> submit_bio(bio);
> -out:
> +
> return ret;
> }
>
> @@ -416,11 +412,6 @@ int swap_readpage(struct page *page, bool synchronous)
>
> ret = 0;
> bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
> - if (bio == NULL) {
> - unlock_page(page);
> - ret = -ENOMEM;
> - goto out;
> - }
> disk = bio->bi_disk;
> /*
> * Keep this task valid during swap readpage because the oom killer may
I'm reluctant to remove these checks - yours is a fairly subtle
discovery and things might change in the future. Intentionally or
otherwise!
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] mm: bio_alloc never fails when set GFP_NOIO, GFP_KERNEL
2020-10-25 19:09 ` Andrew Morton
@ 2020-10-25 19:24 ` Jens Axboe
0 siblings, 0 replies; 4+ messages in thread
From: Jens Axboe @ 2020-10-25 19:24 UTC (permalink / raw)
To: Andrew Morton, Xianting Tian; +Cc: linux-mm, linux-kernel
On 10/25/20 1:09 PM, Andrew Morton wrote:
> On Wed, 21 Oct 2020 11:11:28 +0800 Xianting Tian <tian.xianting@h3c.com> wrote:
>
>> bio_alloc with __GFP_DIRECT_RECLAIM(which is included in GFP_NOIO,
>> GFP_KERNEL) never fails, as stated in the comments of bio_alloc_bioset.
>>
>> So we can remove multiple unneeded null checks of bio_alloc and simplify
>> the code.
>>
>> We have done it in fs/ext4/readpage.c, fs/ext4/page-io.c, fs/direct-io.c,
>> and so forth.
>>
>
> (cc Jens)
>
>> --- a/mm/page_io.c
>> +++ b/mm/page_io.c
>> @@ -30,18 +30,20 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
>> struct page *page, bio_end_io_t end_io)
>> {
>> struct bio *bio;
>> + struct block_device *bdev;
>>
>> + /*
>> + * bio_alloc will _always_ be able to allocate a bio if
>> + * __GFP_DIRECT_RECLAIM is set, see comments for bio_alloc_bioset().
>> + */
>> bio = bio_alloc(gfp_flags, 1);
>> - if (bio) {
>> - struct block_device *bdev;
>> + bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
>> + bio_set_dev(bio, bdev);
>> + bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
>> + bio->bi_end_io = end_io;
>>
>> - bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
>> - bio_set_dev(bio, bdev);
>> - bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
>> - bio->bi_end_io = end_io;
>> + bio_add_page(bio, page, thp_size(page), 0);
>>
>> - bio_add_page(bio, page, thp_size(page), 0);
>> - }
>> return bio;
>> }
>>
>> @@ -351,19 +353,13 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
>>
>> ret = 0;
>> bio = get_swap_bio(GFP_NOIO, page, end_write_func);
>> - if (bio == NULL) {
>> - set_page_dirty(page);
>> - unlock_page(page);
>> - ret = -ENOMEM;
>> - goto out;
>> - }
>> bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
>> bio_associate_blkg_from_page(bio, page);
>> count_swpout_vm_event(page);
>> set_page_writeback(page);
>> unlock_page(page);
>> submit_bio(bio);
>> -out:
>> +
>> return ret;
>> }
>>
>> @@ -416,11 +412,6 @@ int swap_readpage(struct page *page, bool synchronous)
>>
>> ret = 0;
>> bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
>> - if (bio == NULL) {
>> - unlock_page(page);
>> - ret = -ENOMEM;
>> - goto out;
>> - }
>> disk = bio->bi_disk;
>> /*
>> * Keep this task valid during swap readpage because the oom killer may
>
> I'm reluctant to remove these checks - yours is a fairly subtle
> discovery and things might change in the future. Intentionally or
> otherwise!
On the block/bio side, it all boils down to the mempool backing of the
bio allocations. If __GFP_DIRECT_RECLAIM is set for that, then we'll
always wait on allocations for a bio. That is intentional, by design, to
guarantee forward progress. It used to be __GFP_WAIT based, but I guess
that changed at some point...
--
Jens Axboe
^ permalink raw reply [flat|nested] 4+ messages in thread
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2020-10-21 3:11 [PATCH] mm: bio_alloc never fails when set GFP_NOIO, GFP_KERNEL Xianting Tian
2020-10-23 16:40 ` Tianxianting
2020-10-25 19:09 ` Andrew Morton
2020-10-25 19:24 ` Jens Axboe
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