Messages in this thread Patch in this message | | | From | Arnd Bergmann <> | Subject | Re: [PATCH 15/20] ufs: remove the BKL | Date | Thu, 27 Jan 2011 14:13:00 +0100 |
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On Thursday 27 January 2011, Nick Piggin wrote: > On Wed, Jan 26, 2011 at 9:17 AM, Arnd Bergmann <arnd@arndb.de> wrote: > > This introduces a new per-superblock mutex in UFS to replace > > the big kernel lock. I have been careful to avoid nested > > calls to lock_ufs and to get the lock order right with > > respect to other mutexes, in particular lock_super. > > When I looked at removing bkl from minix a long time ago, > I was a bit worried about reclaim and fs/io recursion in some > of the filesystems with bkl.
Thanks for looking at this, you certainly understand these interactions much better than me!
> > @@ -436,7 +439,8 @@ int ufs_getfrag_block(struct inode *inode, sector_t fragment, struct buffer_head > > ret = 0; > > bh = NULL; > > > > - lock_kernel(); > > + if (needs_lock) > > + lock_ufs(sb); > > > > UFSD("ENTER, ino %lu, fragment %llu\n", inode->i_ino, (unsigned long long)fragment); > > if (fragment >
> So, get_block can be called for .writepage in page reclaim, > which takes the lock. ufs_lookup takes the lock and winds > up calling ufs_alloc_inode. And ufs_alloc_inode does > GFP_KERNEL, which can enter reclaim with __GFP_FS > set.
This is one path that I did not consider. My initial thought when you mentioned it was that this is still fine because ufs_getfrag_block can be called with the lock held by the current task, but you are of course right that this won't work when we are called by the writeback task.
> I didn't look through all your filesystem conversions, but it is > something tricky to watch out for I think.
The only other one where I added locks is isofs, and I'm pretty sure that's fine because it's read-only and does not do writeback. HPFS with Andi's suggested solution of making it UP-only is of course also fine.
> Changing everything to GFP_NOFS may be an option, for > such crufty old filesystems...
Yes. All performance optimizations in UFS are pointless anyway as long as we do most of the disk I/O under a global mutex. The patch below converts all allocations that are done under a lock in UFS to GFP_NOFS. If nobody comes up with a better solution, I'll fold that into my other patch.
Arnd ---
fs/ufs/super.c | 8 ++++---- fs/ufs/util.c | 2 +- 2 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/fs/ufs/super.c b/fs/ufs/super.c index e4e06ef..7693d62 100644 --- a/fs/ufs/super.c +++ b/fs/ufs/super.c @@ -539,7 +539,7 @@ static int ufs_read_cylinder_structures(struct super_block *sb) */ size = uspi->s_cssize; blks = (size + uspi->s_fsize - 1) >> uspi->s_fshift; - base = space = kmalloc(size, GFP_KERNEL); + base = space = kmalloc(size, GFP_NOFS); if (!base) goto failed; sbi->s_csp = (struct ufs_csum *)space; @@ -564,7 +564,7 @@ static int ufs_read_cylinder_structures(struct super_block *sb) * Read cylinder group (we read only first fragment from block * at this time) and prepare internal data structures for cg caching. */ - if (!(sbi->s_ucg = kmalloc (sizeof(struct buffer_head *) * uspi->s_ncg, GFP_KERNEL))) + if (!(sbi->s_ucg = kmalloc (sizeof(struct buffer_head *) * uspi->s_ncg, GFP_NOFS))) goto failed; for (i = 0; i < uspi->s_ncg; i++) sbi->s_ucg[i] = NULL; @@ -582,7 +582,7 @@ static int ufs_read_cylinder_structures(struct super_block *sb) ufs_print_cylinder_stuff(sb, (struct ufs_cylinder_group *) sbi->s_ucg[i]->b_data); } for (i = 0; i < UFS_MAX_GROUP_LOADED; i++) { - if (!(sbi->s_ucpi[i] = kmalloc (sizeof(struct ufs_cg_private_info), GFP_KERNEL))) + if (!(sbi->s_ucpi[i] = kmalloc (sizeof(struct ufs_cg_private_info), GFP_NOFS))) goto failed; sbi->s_cgno[i] = UFS_CGNO_EMPTY; } @@ -1415,7 +1415,7 @@ static struct kmem_cache * ufs_inode_cachep; static struct inode *ufs_alloc_inode(struct super_block *sb) { struct ufs_inode_info *ei; - ei = (struct ufs_inode_info *)kmem_cache_alloc(ufs_inode_cachep, GFP_KERNEL); + ei = (struct ufs_inode_info *)kmem_cache_alloc(ufs_inode_cachep, GFP_NOFS); if (!ei) return NULL; ei->vfs_inode.i_version = 1; diff --git a/fs/ufs/util.c b/fs/ufs/util.c index d2c36d5..95425b5 100644 --- a/fs/ufs/util.c +++ b/fs/ufs/util.c @@ -27,7 +27,7 @@ struct ufs_buffer_head * _ubh_bread_ (struct ufs_sb_private_info * uspi, if (count > UFS_MAXFRAG) return NULL; ubh = (struct ufs_buffer_head *) - kmalloc (sizeof (struct ufs_buffer_head), GFP_KERNEL); + kmalloc (sizeof (struct ufs_buffer_head), GFP_NOFS); if (!ubh) return NULL; ubh->fragment = fragment;
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