Re: [f2fs-dev] [PATCH v2] f2fs: avoid congestion_wait when do_checkpointfor better performance

[Gu Zheng]

Hi Jin,

On 10/10/2013 04:09 PM, Jin Xu wrote:

> Hi Gu,
> 
> I have a comment below.
> 
>> Date: Wed, 9 Oct 2013 12:04:09 +0800
>> From: guz.fnst@xxxxxxxxxxxxxx
>> To: yuan.mark.zhong@xxxxxxxxxxx
>> CC: jaegeuk.kim@xxxxxxxxxxx; linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx; shu.tan@xxxxxxxxxxx
>> Subject: Re: [f2fs-dev] [PATCH v2] f2fs: avoid congestion_wait when do_checkpoint for better performance
>>
>> Hi Yuan,
>> On 10/08/2013 07:30 PM, Yuan Zhong wrote:
>>
> ...
>>
>> Signed-off-by: Gu Zheng <guz.fnst@xxxxxxxxxxxxxx>
>> ---
>> fs/f2fs/checkpoint.c | 11 +++++++++--
>> fs/f2fs/f2fs.h | 1 +
>> fs/f2fs/segment.c | 4 ++++
>> 3 files changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>> index d808827..2a5999d 100644
>> --- a/fs/f2fs/checkpoint.c
>> +++ b/fs/f2fs/checkpoint.c
>> @@ -757,8 +757,15 @@ static void do_checkpoint(struct f2fs_sb_info *sbi, bool is_umount)
>> f2fs_put_page(cp_page, 1);
>>
>> /* wait for previous submitted node/meta pages writeback */
>> - while (get_pages(sbi, F2FS_WRITEBACK))
>> - congestion_wait(BLK_RW_ASYNC, HZ / 50);
>> + sbi->cp_task = current;
>> + while (get_pages(sbi, F2FS_WRITEBACK)) {
>> + set_current_state(TASK_UNINTERRUPTIBLE);
>> + if (!get_pages(sbi, F2FS_WRITEBACK))
>> + break;
>> + io_schedule();
>> + }
>> + __set_current_state(TASK_RUNNING);
>> + sbi->cp_task = NULL;
>>
>> filemap_fdatawait_range(sbi->node_inode->i_mapping, 0, LONG_MAX);
>> filemap_fdatawait_range(sbi->meta_inode->i_mapping, 0, LONG_MAX);
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index a955a59..408ace7 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -365,6 +365,7 @@ struct f2fs_sb_info {
>> struct mutex writepages; /* mutex for writepages() */
>> int por_doing; /* recovery is doing or not */
>> int on_build_free_nids; /* build_free_nids is doing */
>> + struct task_struct *cp_task; /* checkpoint task */
>>
>> /* for orphan inode management */
>> struct list_head orphan_inode_list; /* orphan inode list */
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index bd79bbe..3b20359 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -597,6 +597,10 @@ static void f2fs_end_io_write(struct bio *bio, int err)
>>
>> if (p->is_sync)
>> complete(p->wait);
>> +
>> + if (!get_pages(p->sbi, F2FS_WRITEBACK) && p->sbi->cp_task)
>> + wake_up_process(p->sbi->cp_task);
> 
> There is a risk of dereferencing a NULL pointer because here simply comparing the
> cp_task against NULL is not enough to avoid race in multi-thread environment.
> Another thread could have assigned it to NULL in the window between the comparison
> and waking up.

Can not be that, checkpoint routine is always singleton and protected by cp_mutex and cp_rwsem.

Thanks,
Gu

> 
> Regards,
> Jin
>> +
>> kfree(p);
>> bio_put(bio);
>> }
>> --
>> 1.7.7
>>
>> Regards,
>> Gu
>>
>> >
>> >
>> >>> This is a problem here, especially, when sync a large number of small files or dirs.
>> >>> In order to avoid this, a wait_list is introduced,
>> >>> the checkpoint thread will be dropped into the wait_list if the pages have not been written back,
>> >>> and will be waked up by contrast.
>> >
>> >> Please pay some attention to the mail form, this mail is out of format in my mail client.
>> >
>> >> Regards,
>> >> Gu
>> >
>> > Regards,
>> > Yuan
>> >
>> >>>
>> >>> Signed-off-by: Yuan Zhong <yuan.mark.zhong@xxxxxxxxxxx>
>> >>> ---
>> >>> fs/f2fs/checkpoint.c | 3 +--
>> >>> fs/f2fs/f2fs.h | 19 +++++++++++++++++++
>> >>> fs/f2fs/segment.c | 1 +
>> >>> fs/f2fs/super.c | 1 +
>> >>> 4 files changed, 22 insertions(+), 2 deletions(-)
>> >>>
>> >>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>> >>> index ca39442..5d69ae0 100644
>> >>> --- a/fs/f2fs/checkpoint.c
>> >>> +++ b/fs/f2fs/checkpoint.c
>> >>> @@ -758,8 +758,7 @@ static void do_checkpoint(struct f2fs_sb_info *sbi, bool is_umount)
>> >>> f2fs_put_page(cp_page, 1);
>> >>>
>> >>> /* wait for previous submitted node/meta pages writeback */
>> >>> - while (get_pages(sbi, F2FS_WRITEBACK))
>> >>> - congestion_wait(BLK_RW_ASYNC, HZ / 50);
>> >>> + f2fs_writeback_wait(sbi);
>> >>>
>> >>> filemap_fdatawait_range(sbi->node_inode->i_mapping, 0, LONG_MAX);
>> >>> filemap_fdatawait_range(sbi->meta_inode->i_mapping, 0, LONG_MAX);
>> >>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> >>> index 7fd99d8..4b0d70e 100644
>> >>> --- a/fs/f2fs/f2fs.h
>> >>> +++ b/fs/f2fs/f2fs.h
>> >>> @@ -18,6 +18,8 @@
>> >>> #include <linux/crc32.h>
>> >>> #include <linux/magic.h>
>> >>> #include <linux/kobject.h>
>> >>> +#include <linux/wait.h>
>> >>> +#include <linux/sched.h>
>> >>>
>> >>> /*
>> >>> * For mount options
>> >>> @@ -368,6 +370,7 @@ struct f2fs_sb_info {
>> >>> struct mutex fs_lock[NR_GLOBAL_LOCKS]; /* blocking FS operations */
>> >>> struct mutex node_write; /* locking node writes */
>> >>> struct mutex writepages; /* mutex for writepages() */
>> >>> + wait_queue_head_t writeback_wqh; /* wait_queue for writeback */
>> >>> unsigned char next_lock_num; /* round-robin global locks */
>> >>> int por_doing; /* recovery is doing or not */
>> >>> int on_build_free_nids; /* build_free_nids is doing */
>> >>> @@ -961,6 +964,22 @@ static inline int f2fs_readonly(struct super_block *sb)
>> >>> return sb->s_flags & MS_RDONLY;
>> >>> }
>> >>>
>> >>> +static inline void f2fs_writeback_wait(struct f2fs_sb_info *sbi)
>> >>> +{
>> >>> + DEFINE_WAIT(wait);
>> >>> +
>> >>> + prepare_to_wait(&sbi->writeback_wqh, &wait, TASK_UNINTERRUPTIBLE);
>> >>> + if (get_pages(sbi, F2FS_WRITEBACK))
>> >>> + io_schedule();
>> >>> + finish_wait(&sbi->writeback_wqh, &wait);
>> >>> +}
>> >>> +
>> >>> +static inline void f2fs_writeback_wake(struct f2fs_sb_info *sbi)
>> >>> +{
>> >>> + if (!get_pages(sbi, F2FS_WRITEBACK))
>> >>> + wake_up_all(&sbi->writeback_wqh);
>> >>> +}
>> >>> +
>> >>> /*
>> >>> * file.c
>> >>> */
>> >>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> >>> index bd79bbe..0708aa9 100644
>> >>> --- a/fs/f2fs/segment.c
>> >>> +++ b/fs/f2fs/segment.c
>> >>> @@ -597,6 +597,7 @@ static void f2fs_end_io_write(struct bio *bio, int err)
>> >>>
>> >>> if (p->is_sync)
>> >>> complete(p->wait);
>> >>> + f2fs_writeback_wake(p->sbi);
>> >>> kfree(p);
>> >>> bio_put(bio);
>> >>> }
>> >>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>> >>> index 094ccc6..3ac6d85 100644
>> >>> --- a/fs/f2fs/super.c
>> >>> +++ b/fs/f2fs/super.c
>> >>> @@ -835,6 +835,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>> >>> mutex_init(&sbi->gc_mutex);
>> >>> mutex_init(&sbi->writepages);
>> >>> mutex_init(&sbi->cp_mutex);
>> >>> + init_waitqueue_head(&sbi->writeback_wqh);
>> >>> for (i = 0; i < NR_GLOBAL_LOCKS; i++)
>> >>> mutex_init(&sbi->fs_lock[i]);
>> >>> mutex_init(&sbi->node_write);N‹§²æìr¸›yúèšØb²X¬¶Ç§vØ^–)Þº{.nÇ+‰·¥Š{±‘êçzX§¶›¡Ü¨}©ž²Æ zÚ&j:+v‰¨¾«‘êçzZ+€Ê+zf£¢·hšˆ§~†­†Ûiÿûàz¹®w¥¢¸?™¨è­Ú&¢)ߢf”ù^jÇ«y§m…á@A«a¶Úÿ0¶ìh®å’i
>>
>>
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