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

Gao Xiang
2019-10-30T10:41:16Z

On Wed, Oct 30, 2019 at 05:27:54PM +0800, Chao Yu wrote:
> 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 ...

Okay, hope to get hints from Jaegeuk and redo this patch then...

Thanks,
Gao Xiang

>
> 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",
> >>>
> > .
> >