On 2015-03-14 04:51, Ryusuke Konishi wrote:
> On Tue, 24 Feb 2015 20:01:44 +0100, Andreas Rohner wrote:
>> It doesn't really matter if the number of reclaimable blocks for a
>> segment is inaccurate, as long as the overall performance is better than
>> the simple timestamp algorithm and starvation is prevented.
>>
>> The following steps will lead to starvation of a segment:
>>
>> 1. The segment is written
>> 2. A snapshot is created
>> 3. The files in the segment are deleted and the number of live
>> blocks for the segment is decremented to a very low value
>> 4. The GC tries to free the segment, but there are no reclaimable
>> blocks, because they are all protected by the snapshot. To prevent an
>> infinite loop the GC has to adjust the number of live blocks to the
>> correct value.
>> 5. The snapshot is converted to a checkpoint and the blocks in the
>> segment are now reclaimable.
>> 6. The GC will never attemt to clean the segment again, because of it
>> incorrectly shows up as having a high number of live blocks.
>>
>> To prevent this, the already existing padding field of the SUFILE entry
>> is used to track the number of snapshot blocks in the segment. This
>> number is only set by the GC, since it collects the necessary
>> information anyway. So there is no need, to track which block belongs to
>> which segment. In step 4 of the list above the GC will set the new field
>> su_nsnapshot_blks. In step 5 all entries in the SUFILE are checked and
>> entries with a big su_nsnapshot_blks field get their su_nlive_blks field
>> reduced.
>>
>> Signed-off-by: Andreas Rohner <andreas.roh...@gmx.net>
>> ---
>> fs/nilfs2/cpfile.c | 5 ++
>> fs/nilfs2/segbuf.c | 1 +
>> fs/nilfs2/segbuf.h | 1 +
>> fs/nilfs2/segment.c | 7 ++-
>> fs/nilfs2/sufile.c | 114
>> ++++++++++++++++++++++++++++++++++++++++++----
>> fs/nilfs2/sufile.h | 4 +-
>> fs/nilfs2/the_nilfs.h | 7 +++
>> include/linux/nilfs2_fs.h | 12 +++--
>> 8 files changed, 136 insertions(+), 15 deletions(-)
>>
>> diff --git a/fs/nilfs2/cpfile.c b/fs/nilfs2/cpfile.c
>> index 0d58075..6b61fd7 100644
>> --- a/fs/nilfs2/cpfile.c
>> +++ b/fs/nilfs2/cpfile.c
>> @@ -28,6 +28,7 @@
>> #include <linux/nilfs2_fs.h>
>> #include "mdt.h"
>> #include "cpfile.h"
>> +#include "sufile.h"
>>
>>
>> static inline unsigned long
>> @@ -703,6 +704,7 @@ static int nilfs_cpfile_clear_snapshot(struct inode
>> *cpfile, __u64 cno)
>> struct nilfs_cpfile_header *header;
>> struct nilfs_checkpoint *cp;
>> struct nilfs_snapshot_list *list;
>> + struct the_nilfs *nilfs = cpfile->i_sb->s_fs_info;
>> __u64 next, prev;
>> void *kaddr;
>> int ret;
>> @@ -784,6 +786,9 @@ static int nilfs_cpfile_clear_snapshot(struct inode
>> *cpfile, __u64 cno)
>> mark_buffer_dirty(header_bh);
>> nilfs_mdt_mark_dirty(cpfile);
>>
>> + if (nilfs_feature_track_snapshots(nilfs))
>> + nilfs_sufile_fix_starving_segs(nilfs->ns_sufile);
>> +
>> brelse(prev_bh);
>>
>> out_next:
>> diff --git a/fs/nilfs2/segbuf.c b/fs/nilfs2/segbuf.c
>> index bbd807b..a98c576 100644
>> --- a/fs/nilfs2/segbuf.c
>> +++ b/fs/nilfs2/segbuf.c
>> @@ -59,6 +59,7 @@ struct nilfs_segment_buffer *nilfs_segbuf_new(struct
>> super_block *sb)
>> segbuf->sb_super_root = NULL;
>> segbuf->sb_nlive_blks_added = 0;
>> segbuf->sb_nlive_blks_diff = 0;
>> + segbuf->sb_nsnapshot_blks = 0;
>>
>> init_completion(&segbuf->sb_bio_event);
>> atomic_set(&segbuf->sb_err, 0);
>> diff --git a/fs/nilfs2/segbuf.h b/fs/nilfs2/segbuf.h
>> index 4e994f7..7a462c4 100644
>> --- a/fs/nilfs2/segbuf.h
>> +++ b/fs/nilfs2/segbuf.h
>> @@ -85,6 +85,7 @@ struct nilfs_segment_buffer {
>> unsigned sb_rest_blocks;
>> __u32 sb_nlive_blks_added;
>> __s64 sb_nlive_blks_diff;
>> + __u32 sb_nsnapshot_blks;
>>
>> /* Buffers */
>> struct list_head sb_segsum_buffers;
>> diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
>> index 16c7c36..b976198 100644
>> --- a/fs/nilfs2/segment.c
>> +++ b/fs/nilfs2/segment.c
>> @@ -1381,6 +1381,7 @@ static void nilfs_segctor_update_segusage(struct
>> nilfs_sc_info *sci,
>> (segbuf->sb_pseg_start - segbuf->sb_fseg_start);
>> ret = nilfs_sufile_set_segment_usage(sufile, segbuf->sb_segnum,
>> live_blocks,
>> + segbuf->sb_nsnapshot_blks,
>> sci->sc_seg_ctime);
>> WARN_ON(ret); /* always succeed because the segusage is dirty */
>>
>> @@ -1405,7 +1406,7 @@ static void nilfs_cancel_segusage(struct list_head
>> *logs,
>> segbuf = NILFS_FIRST_SEGBUF(logs);
>> ret = nilfs_sufile_set_segment_usage(sufile, segbuf->sb_segnum,
>> segbuf->sb_pseg_start -
>> - segbuf->sb_fseg_start, 0);
>> + segbuf->sb_fseg_start, 0, 0);
>> WARN_ON(ret); /* always succeed because the segusage is dirty */
>>
>> if (nilfs_feature_track_live_blks(nilfs))
>> @@ -1416,7 +1417,7 @@ static void nilfs_cancel_segusage(struct list_head
>> *logs,
>>
>> list_for_each_entry_continue(segbuf, logs, sb_list) {
>> ret = nilfs_sufile_set_segment_usage(sufile, segbuf->sb_segnum,
>> - 0, 0);
>> + 0, 0, 0);
>> WARN_ON(ret); /* always succeed */
>> }
>> }
>> @@ -1521,6 +1522,8 @@ static void nilfs_segctor_dec_nlive_blks_gc(struct
>> inode *dat,
>>
>> if (!buffer_nilfs_snapshot(bh) && isreclaimable)
>> segbuf->sb_nlive_blks_diff--;
>> + if (buffer_nilfs_snapshot(bh))
>> + segbuf->sb_nsnapshot_blks++;
>> }
>>
>> /**
>> diff --git a/fs/nilfs2/sufile.c b/fs/nilfs2/sufile.c
>> index 574a77e..a6dc7bf 100644
>> --- a/fs/nilfs2/sufile.c
>> +++ b/fs/nilfs2/sufile.c
>> @@ -468,7 +468,7 @@ void nilfs_sufile_do_scrap(struct inode *sufile, __u64
>> *data,
>> su->su_flags = cpu_to_le32(1UL << NILFS_SEGMENT_USAGE_DIRTY);
>> if (nilfs_sufile_ext_supported(sufile)) {
>> su->su_nlive_blks = cpu_to_le32(0);
>> - su->su_pad = cpu_to_le32(0);
>> + su->su_nsnapshot_blks = cpu_to_le32(0);
>> su->su_nlive_lastmod = cpu_to_le64(0);
>> }
>> kunmap_atomic(kaddr);
>> @@ -538,7 +538,8 @@ int nilfs_sufile_mark_dirty(struct inode *sufile, __u64
>> segnum)
>> * @modtime: modification time (option)
>> */
>> int nilfs_sufile_set_segment_usage(struct inode *sufile, __u64 segnum,
>> - unsigned long nblocks, time_t modtime)
>> + unsigned long nblocks, __u32 nsnapshot_blks,
>> + time_t modtime)
>> {
>> struct buffer_head *bh;
>> struct nilfs_segment_usage *su;
>> @@ -556,9 +557,18 @@ int nilfs_sufile_set_segment_usage(struct inode
>> *sufile, __u64 segnum,
>> if (modtime)
>> su->su_lastmod = cpu_to_le64(modtime);
>> su->su_nblocks = cpu_to_le32(nblocks);
>> - if (nilfs_sufile_ext_supported(sufile) &&
>> - nblocks < le32_to_cpu(su->su_nlive_blks))
>> - su->su_nlive_blks = su->su_nblocks;
>> + if (nilfs_sufile_ext_supported(sufile)) {
>> + if (nblocks < le32_to_cpu(su->su_nlive_blks))
>> + su->su_nlive_blks = su->su_nblocks;
>> +
>> + nsnapshot_blks += le32_to_cpu(su->su_nsnapshot_blks);
>> +
>> + if (nblocks < nsnapshot_blks)
>> + nsnapshot_blks = nblocks;
>> +
>> + su->su_nsnapshot_blks = cpu_to_le32(nsnapshot_blks);
>> + }
>> +
>> kunmap_atomic(kaddr);
>>
>> mark_buffer_dirty(bh);
>> @@ -891,7 +901,7 @@ ssize_t nilfs_sufile_get_suinfo(struct inode *sufile,
>> __u64 segnum, void *buf,
>>
>> if (sisz >= NILFS_EXT_SUINFO_SIZE) {
>> si->sui_nlive_blks = nlb;
>> - si->sui_pad = 0;
>> + si->sui_nsnapshot_blks = 0;
>> si->sui_nlive_lastmod = lm;
>> }
>> }
>> @@ -939,6 +949,7 @@ ssize_t nilfs_sufile_set_suinfo(struct inode *sufile,
>> void *buf,
>> int ret = 0;
>> bool sup_ext = (supsz >= NILFS_EXT_SUINFO_UPDATE_SIZE);
>> bool su_ext = nilfs_sufile_ext_supported(sufile);
>> + bool supsu_ext = sup_ext && su_ext;
>>
>> if (unlikely(nsup == 0))
>> return ret;
>> @@ -952,6 +963,10 @@ ssize_t nilfs_sufile_set_suinfo(struct inode *sufile,
>> void *buf,
>> nilfs->ns_blocks_per_segment)
>> || (nilfs_suinfo_update_nlive_blks(sup) && sup_ext &&
>> sup->sup_sui.sui_nlive_blks >
>> + nilfs->ns_blocks_per_segment)
>> + || (nilfs_suinfo_update_nsnapshot_blks(sup) &&
>> + sup_ext &&
>> + sup->sup_sui.sui_nsnapshot_blks >
>> nilfs->ns_blocks_per_segment))
>> return -EINVAL;
>> }
>> @@ -979,11 +994,15 @@ ssize_t nilfs_sufile_set_suinfo(struct inode *sufile,
>> void *buf,
>> if (nilfs_suinfo_update_nblocks(sup))
>> su->su_nblocks = cpu_to_le32(sup->sup_sui.sui_nblocks);
>>
>> - if (nilfs_suinfo_update_nlive_blks(sup) && sup_ext && su_ext)
>> + if (nilfs_suinfo_update_nlive_blks(sup) && supsu_ext)
>> su->su_nlive_blks =
>> cpu_to_le32(sup->sup_sui.sui_nlive_blks);
>>
>> - if (nilfs_suinfo_update_nlive_lastmod(sup) && sup_ext && su_ext)
>> + if (nilfs_suinfo_update_nsnapshot_blks(sup) && supsu_ext)
>> + su->su_nsnapshot_blks =
>> + cpu_to_le32(sup->sup_sui.sui_nsnapshot_blks);
>> +
>> + if (nilfs_suinfo_update_nlive_lastmod(sup) && supsu_ext)
>> su->su_nlive_lastmod =
>> cpu_to_le64(sup->sup_sui.sui_nlive_lastmod);
>>
>> @@ -1050,6 +1069,85 @@ ssize_t nilfs_sufile_set_suinfo(struct inode *sufile,
>> void *buf,
>> }
>>
>> /**
>> + * nilfs_sufile_fix_starving_segs - fix potentially starving segments
>> + * @sufile: inode of segment usage file
>> + *
>> + * Description: Scans for segments, which are potentially starving and
>> + * reduces the number of live blocks to less than half of the maximum
>> + * number of blocks in a segment. This way the segment is more likely to be
>> + * chosen by the GC. A segment is marked as potentially starving, if more
>> + * than half of the blocks it contains are protected by snapshots.
>> + *
>> + * Return Value: On success, 0 is returned and on error, one of the
>> + * following negative error codes is returned.
>> + *
>> + * %-EIO - I/O error.
>> + *
>> + * %-ENOMEM - Insufficient amount of memory available.
>> + */
>> +int nilfs_sufile_fix_starving_segs(struct inode *sufile)
>> +{
>> + struct buffer_head *su_bh;
>> + struct nilfs_segment_usage *su;
>> + size_t n, i, susz = NILFS_MDT(sufile)->mi_entry_size;
>> + struct the_nilfs *nilfs = sufile->i_sb->s_fs_info;
>> + void *kaddr;
>> + unsigned long nsegs, segusages_per_block;
>> + __u32 max_segblks = nilfs->ns_blocks_per_segment / 2;
>> + __u64 segnum = 0;
>> + int ret = 0, blkdirty, dirty = 0;
>> +
>> + down_write(&NILFS_MDT(sufile)->mi_sem);
>> +
>> + segusages_per_block = nilfs_sufile_segment_usages_per_block(sufile);
>> + nsegs = nilfs_sufile_get_nsegments(sufile);
>> +
>> + while (segnum < nsegs) {
>> + n = nilfs_sufile_segment_usages_in_block(sufile, segnum,
>> + nsegs - 1);
>> +
>> + ret = nilfs_sufile_get_segment_usage_block(sufile, segnum,
>> + 0, &su_bh);
>> + if (ret < 0) {
>> + if (ret != -ENOENT)
>> + goto out;
>> + /* hole */
>> + segnum += n;
>> + continue;
>> + }
>> +
>> + kaddr = kmap_atomic(su_bh->b_page);
>> + su = nilfs_sufile_block_get_segment_usage(sufile, segnum,
>> + su_bh, kaddr);
>> + blkdirty = 0;
>> + for (i = 0; i < n; ++i, ++segnum, su = (void *)su + susz) {
>> + if (le32_to_cpu(su->su_nsnapshot_blks) <= max_segblks)
>> + continue;
>> +
>> + if (su->su_nlive_blks <= max_segblks)
>> + continue;
>> +
>> + su->su_nlive_blks = max_segblks;
>> + blkdirty = 1;
>> + }
>> +
>> + kunmap_atomic(kaddr);
>> + if (blkdirty) {
>> + mark_buffer_dirty(su_bh);
>> + dirty = 1;
>> + }
>> + put_bh(su_bh);
>> + }
>> +
>> +out:
>> + if (dirty)
>> + nilfs_mdt_mark_dirty(sufile);
>> +
>> + up_write(&NILFS_MDT(sufile)->mi_sem);
>> + return ret;
>> +}
>> +
>> +/**
>> * nilfs_sufile_trim_fs() - trim ioctl handle function
>> * @sufile: inode of segment usage file
>> * @range: fstrim_range structure
>> diff --git a/fs/nilfs2/sufile.h b/fs/nilfs2/sufile.h
>> index ae3c52a..e831622 100644
>> --- a/fs/nilfs2/sufile.h
>> +++ b/fs/nilfs2/sufile.h
>> @@ -45,7 +45,8 @@ int nilfs_sufile_set_alloc_range(struct inode *sufile,
>> __u64 start, __u64 end);
>> int nilfs_sufile_alloc(struct inode *, __u64 *);
>> int nilfs_sufile_mark_dirty(struct inode *sufile, __u64 segnum);
>> int nilfs_sufile_set_segment_usage(struct inode *sufile, __u64 segnum,
>> - unsigned long nblocks, time_t modtime);
>> + unsigned long nblocks, __u32 nsnapshot_blks,
>> + time_t modtime);
>> int nilfs_sufile_get_stat(struct inode *, struct nilfs_sustat *);
>> ssize_t nilfs_sufile_get_suinfo(struct inode *, __u64, void *, unsigned,
>> size_t);
>> @@ -72,6 +73,7 @@ int nilfs_sufile_resize(struct inode *sufile, __u64
>> newnsegs);
>> int nilfs_sufile_read(struct super_block *sb, size_t susize,
>> struct nilfs_inode *raw_inode, struct inode **inodep);
>> int nilfs_sufile_trim_fs(struct inode *sufile, struct fstrim_range *range);
>> +int nilfs_sufile_fix_starving_segs(struct inode *);
>>
>> /**
>> * nilfs_sufile_scrap - make a segment garbage
>> diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
>> index 87cab10..3d495f1 100644
>> --- a/fs/nilfs2/the_nilfs.h
>> +++ b/fs/nilfs2/the_nilfs.h
>> @@ -409,4 +409,11 @@ static inline int nilfs_feature_track_live_blks(struct
>> the_nilfs *nilfs)
>> NILFS_FEATURE_COMPAT_SUFILE_EXTENSION);
>> }
>>
>> +static inline int nilfs_feature_track_snapshots(struct the_nilfs *nilfs)
>> +{
>> + return (nilfs->ns_feature_compat &
>> + NILFS_FEATURE_COMPAT_TRACK_SNAPSHOTS) &&
>> + nilfs_feature_track_live_blks(nilfs);
>> +}
>> +
>> #endif /* _THE_NILFS_H */
>> diff --git a/include/linux/nilfs2_fs.h b/include/linux/nilfs2_fs.h
>> index 6ffdc09..a3c7593 100644
>> --- a/include/linux/nilfs2_fs.h
>> +++ b/include/linux/nilfs2_fs.h
>> @@ -222,11 +222,13 @@ struct nilfs_super_block {
>> */
>> #define NILFS_FEATURE_COMPAT_SUFILE_EXTENSION (1ULL << 0)
>> #define NILFS_FEATURE_COMPAT_TRACK_LIVE_BLKS (1ULL << 1)
>> +#define NILFS_FEATURE_COMPAT_TRACK_SNAPSHOTS (1ULL << 2)
>>
>> #define NILFS_FEATURE_COMPAT_RO_BLOCK_COUNT (1ULL << 0)
>>
>> #define NILFS_FEATURE_COMPAT_SUPP (NILFS_FEATURE_COMPAT_SUFILE_EXTENSION \
>> - | NILFS_FEATURE_COMPAT_TRACK_LIVE_BLKS)
>> + | NILFS_FEATURE_COMPAT_TRACK_LIVE_BLKS \
>> + | NILFS_FEATURE_COMPAT_TRACK_SNAPSHOTS)
>> #define NILFS_FEATURE_COMPAT_RO_SUPP
>> NILFS_FEATURE_COMPAT_RO_BLOCK_COUNT
>> #define NILFS_FEATURE_INCOMPAT_SUPP 0ULL
>>
>
> You don't have to add three compat flags just for this one patchset.
> Please unify it.
>
> #define NILFS_FEATURE_COMPAT_TRACK_LIVE_BLKS (1ULL << 0)
>
> looks to be enough.
I could merge the TRACK_LIVE_BLKS and TRACK_SNAPSHOTS flag, but I would
suggest to at least leave the SUFILE_EXTENSION flag (maybe with a
different name). The SUFILE_EXTENSION flag has to be set at mkfs time
and it cannot be set or removed later, because you cannot change the on
disk format later. I actually set SUFILE_EXTENSION by default in mkfs,
because it is not harmful and it gives the user the option to switch the
other flags on later.
Regards,
Andreas Rohner
> Regards,
> Ryusuke Konishi
>
>
>> @@ -630,7 +632,7 @@ struct nilfs_segment_usage {
>> __le32 su_nblocks;
>> __le32 su_flags;
>> __le32 su_nlive_blks;
>> - __le32 su_pad;
>> + __le32 su_nsnapshot_blks;
>> __le64 su_nlive_lastmod;
>> };
>>
>> @@ -682,7 +684,7 @@ nilfs_segment_usage_set_clean(struct nilfs_segment_usage
>> *su, size_t susz)
>> su->su_flags = cpu_to_le32(0);
>> if (susz >= NILFS_EXT_SEGMENT_USAGE_SIZE) {
>> su->su_nlive_blks = cpu_to_le32(0);
>> - su->su_pad = cpu_to_le32(0);
>> + su->su_nsnapshot_blks = cpu_to_le32(0);
>> su->su_nlive_lastmod = cpu_to_le64(0);
>> }
>> }
>> @@ -723,7 +725,7 @@ struct nilfs_suinfo {
>> __u32 sui_nblocks;
>> __u32 sui_flags;
>> __u32 sui_nlive_blks;
>> - __u32 sui_pad;
>> + __u32 sui_nsnapshot_blks;
>> __u64 sui_nlive_lastmod;
>> };
>>
>> @@ -770,6 +772,7 @@ enum {
>> NILFS_SUINFO_UPDATE_FLAGS,
>> NILFS_SUINFO_UPDATE_NLIVE_BLKS,
>> NILFS_SUINFO_UPDATE_NLIVE_LASTMOD,
>> + NILFS_SUINFO_UPDATE_NSNAPSHOT_BLKS,
>> __NR_NILFS_SUINFO_UPDATE_FIELDS,
>> };
>>
>> @@ -794,6 +797,7 @@ NILFS_SUINFO_UPDATE_FNS(LASTMOD, lastmod)
>> NILFS_SUINFO_UPDATE_FNS(NBLOCKS, nblocks)
>> NILFS_SUINFO_UPDATE_FNS(FLAGS, flags)
>> NILFS_SUINFO_UPDATE_FNS(NLIVE_BLKS, nlive_blks)
>> +NILFS_SUINFO_UPDATE_FNS(NSNAPSHOT_BLKS, nsnapshot_blks)
>> NILFS_SUINFO_UPDATE_FNS(NLIVE_LASTMOD, nlive_lastmod)
>>
>> #define NILFS_MIN_SUINFO_UPDATE_SIZE \
>> --
>> 2.3.0
>>
>> --
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>
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