Messages in this thread | | | From | Daeho Jeong <> | Date | Fri, 12 Mar 2021 23:37:29 +0900 | Subject | Re: [PATCH v4] f2fs: add sysfs nodes to get runtime compression stat |
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As you can see, if we're doing like the below.
sbi->compr_written_block += blocks;
Let's assume the initial value as 0.
<thread A> <thread B> sbi->compr_written_block = 0;
sbi->compr_written_block = 0; +blocks(3); + blocks(2); sbi->compr_written_block = 3;
sbi->compr_written_block = 2;
Finally, we end up with 2, not 5.
As more threads are participating it, we might miss more counting.
2021년 3월 12일 (금) 오후 11:04, Greg KH <gregkh@linuxfoundation.org>님이 작성: > > On Fri, Mar 12, 2021 at 10:56:13PM +0900, Daeho Jeong wrote: > > Thanks for suggesting me sysfs_emit(). > > > > For atomic values, actually, those are needed for writer part, not reader. > > > > +#define add_compr_block_stat(inode, blocks) \ > > + do { \ > > + struct f2fs_sb_info *sbi = F2FS_I_SB(inode); \ > > + int diff = F2FS_I(inode)->i_cluster_size - blocks; \ > > + atomic64_add(blocks, &sbi->compr_written_block); \ > > + atomic64_add(diff, &sbi->compr_saved_block); \ > > + } while (0) > > > > I needed a protection here, because they might be updated in the race condition. > > Why? What are you trying to protect from "racing" here? > > thanks, > > greg k-h
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