Re: [f2fs-dev] [PATCH] f2fs: bio_alloc should never fail

Chao Yu
2019-10-30T09:28:14Z

Hi Xiang,

On 2019/10/30 17:15, Gao Xiang wrote:
> Hi Chao,
>
> On Wed, Oct 30, 2019 at 04:56:17PM +0800, Chao Yu wrote:
>> On 2019/10/30 11:55, Gao Xiang wrote:
>>> remove such useless code and related fault injection.
>>
>> Hi Xiang,
>>
>> Although, there is so many 'nofail' allocation in f2fs, I think we'd better
>> avoid such allocation as much as possible (now for read path, we may allow to
>> fail to allocate bio), I suggest to keep the failure path and bio allocation
>> injection.
>>
>> It looks bio_alloc() will use its own mempool, which may suffer deadlock
>> potentially. So how about changing to use bio_alloc_bioset(, , NULL) instead of
>> bio_alloc()?
>
> Yes, I noticed the original commit 740432f83560 ("f2fs: handle failed bio allocation"),
> yet I don't find any real call trace clue what happened before.
>
> As my understanding, if we allocate bios without submit_bio (I mean write path) with
> default bs and gfp_flags GFP_NOIO or GFP_KERNEL, I think it will be slept inside
> mempool rather than return NULL to its caller... Please correct me if I'm wrong...

I'm curious too...

Jaegeuk may know the details.

>
> I could send another patch with bio_alloc_bioset(, , NULL), I am curious to know the
> original issue and how it solved though...
>
> For read or flush path, since it will submit_bio and bio_alloc one by one, I think
> mempool will get a page quicker (memory failure path could be longer). But I can
> send a patch just by using bio_alloc_bioset(, , NULL) instead as you suggested later.

You're right, in low memory scenario, allocation with bioset will be faster, as
you mentioned offline, maybe we can add/use a priviate bioset like btrfs did
rather than using global one, however, we'd better check how deadlock happen
with a bioset mempool first ...

Thanks,

>
> Thanks,
> Gao Xiang
>
>>
>> Thanks,
>>
>>>
>>> Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
>>> ---
>>> Documentation/filesystems/f2fs.txt | 1 -
>>> fs/f2fs/data.c | 6 ++----
>>> fs/f2fs/f2fs.h | 21 ---------------------
>>> fs/f2fs/segment.c | 5 +----
>>> fs/f2fs/super.c | 1 -
>>> 5 files changed, 3 insertions(+), 31 deletions(-)
>>>
>>> diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt
>>> index 7e1991328473..3477c3e4c08b 100644
>>> --- a/Documentation/filesystems/f2fs.txt
>>> +++ b/Documentation/filesystems/f2fs.txt
>>> @@ -172,7 +172,6 @@ fault_type=%d Support configuring fault injection type, should be
>>> FAULT_KVMALLOC 0x000000002
>>> FAULT_PAGE_ALLOC 0x000000004
>>> FAULT_PAGE_GET 0x000000008
>>> - FAULT_ALLOC_BIO 0x000000010
>>> FAULT_ALLOC_NID 0x000000020
>>> FAULT_ORPHAN 0x000000040
>>> FAULT_BLOCK 0x000000080
>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>> index 5755e897a5f0..3b88dcb15de6 100644
>>> --- a/fs/f2fs/data.c
>>> +++ b/fs/f2fs/data.c
>>> @@ -288,7 +288,7 @@ static struct bio *__bio_alloc(struct f2fs_io_info *fio, int npages)
>>> struct f2fs_sb_info *sbi = fio->sbi;
>>> struct bio *bio;
>>>
>>> - bio = f2fs_bio_alloc(sbi, npages, true);
>>> + bio = bio_alloc(GFP_NOIO, npages);
>>>
>>> f2fs_target_device(sbi, fio->new_blkaddr, bio);
>>> if (is_read_io(fio->op)) {
>>> @@ -682,9 +682,7 @@ static struct bio *f2fs_grab_read_bio(struct inode *inode, block_t blkaddr,
>>> struct bio_post_read_ctx *ctx;
>>> unsigned int post_read_steps = 0;
>>>
>>> - bio = f2fs_bio_alloc(sbi, min_t(int, nr_pages, BIO_MAX_PAGES), false);
>>> - if (!bio)
>>> - return ERR_PTR(-ENOMEM);
>>> + bio = bio_alloc(GFP_KERNEL, min_t(int, nr_pages, BIO_MAX_PAGES));
>>> f2fs_target_device(sbi, blkaddr, bio);
>>> bio->bi_end_io = f2fs_read_end_io;
>>> bio_set_op_attrs(bio, REQ_OP_READ, op_flag);
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index 4024790028aa..40012f874be0 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -44,7 +44,6 @@ enum {
>>> FAULT_KVMALLOC,
>>> FAULT_PAGE_ALLOC,
>>> FAULT_PAGE_GET,
>>> - FAULT_ALLOC_BIO,
>>> FAULT_ALLOC_NID,
>>> FAULT_ORPHAN,
>>> FAULT_BLOCK,
>>> @@ -2210,26 +2209,6 @@ static inline void *f2fs_kmem_cache_alloc(struct kmem_cache *cachep,
>>> return entry;
>>> }
>>>
>>> -static inline struct bio *f2fs_bio_alloc(struct f2fs_sb_info *sbi,
>>> - int npages, bool no_fail)
>>> -{
>>> - struct bio *bio;
>>> -
>>> - if (no_fail) {
>>> - /* No failure on bio allocation */
>>> - bio = bio_alloc(GFP_NOIO, npages);
>>> - if (!bio)
>>> - bio = bio_alloc(GFP_NOIO | __GFP_NOFAIL, npages);
>>> - return bio;
>>> - }
>>> - if (time_to_inject(sbi, FAULT_ALLOC_BIO)) {
>>> - f2fs_show_injection_info(FAULT_ALLOC_BIO);
>>> - return NULL;
>>> - }
>>> -
>>> - return bio_alloc(GFP_KERNEL, npages);
>>> -}
>>> -
>>> static inline bool is_idle(struct f2fs_sb_info *sbi, int type)
>>> {
>>> if (sbi->gc_mode == GC_URGENT)
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 808709581481..28457c878d0d 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -552,10 +552,7 @@ static int __submit_flush_wait(struct f2fs_sb_info *sbi,
>>> struct bio *bio;
>>> int ret;
>>>
>>> - bio = f2fs_bio_alloc(sbi, 0, false);
>>> - if (!bio)
>>> - return -ENOMEM;
>>> -
>>> + bio = bio_alloc(GFP_KERNEL, 0);
>>> bio->bi_opf = REQ_OP_WRITE | REQ_SYNC | REQ_PREFLUSH;
>>> bio_set_dev(bio, bdev);
>>> ret = submit_bio_wait(bio);
>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>> index 1443cee15863..51945dd27f00 100644
>>> --- a/fs/f2fs/super.c
>>> +++ b/fs/f2fs/super.c
>>> @@ -44,7 +44,6 @@ const char *f2fs_fault_name[FAULT_MAX] = {
>>> [FAULT_KVMALLOC] = "kvmalloc",
>>> [FAULT_PAGE_ALLOC] = "page alloc",
>>> [FAULT_PAGE_GET] = "page get",
>>> - [FAULT_ALLOC_BIO] = "alloc bio",
>>> [FAULT_ALLOC_NID] = "alloc nid",
>>> [FAULT_ORPHAN] = "orphan",
>>> [FAULT_BLOCK] = "no more block",
>>>
> .
>