linux-kernel - Re: [PATCH] f2fs: fix to name f2fs GC task as per partition instead of per device

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Date:	Wed, 06 Feb 2013 18:21:46 +0900
From:	Jaegeuk Kim <jaegeuk.kim@...sung.com>
To:	Namjae Jeon <linkinjeon@...il.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Amit Sahrawat <a.sahrawat@...sung.com>
Subject: Re: [PATCH] f2fs: fix to name f2fs GC task as per partition instead of
 per device

Hi,

2013-02-06 (수), 13:59 +0900, Namjae Jeon:
> 2013/2/6, Jaegeuk Kim <jaegeuk.kim@...sung.com>:
> > Hi,
> >
> > How about this?
> >
> > 2013-02-05 (화), 23:24 +0900, Namjae Jeon:
> >> From: Namjae Jeon <namjae.jeon@...sung.com>
> >>
> >> After the commit 2184ad190a79ae2b40b5f5db1fbde5c22db6d310, it allowed
> >> for naming GC threads based on the device.
> >> i.e., if we have F2FS formatted partition in different devices - we will
> >> have their GC thread names after the device. But, when we have a case
> >> like
> >> 2 or more partitions on the same device having F2FS filesystem.
> >> In that case we are not able to differentiate between the GC threads.
> >> So, to differentiate at all possible levels we can use the major/minor of
> >> the device to have unique identification in the name.
> >>
> >> Before patch:
> >> root  9726  0.0  0.0  0  0 ?  S  14:32   0:00 [f2fs_gc-8:48]
> >> root  9736  0.0  0.0  0  0 ?  S  14:32   0:00 [f2fs_gc-8:16]
> >> root  9892  0.0  0.0  0  0 ?  S  14:33   0:00 [f2fs_gc-8:32]
> >> root  9907  0.0  0.0  0  0 ?  S  14:34   0:00 [f2fs_gc-8:32]
> >>
> >> After Patch:
> >> root  16756  0.0  0.0  0  0 ?  S  14:57   0:00 [f2fs_gc-8:18]
> >> root  16765  0.0  0.0  0  0 ?  S  14:57   0:00 [f2fs_gc-8:19]
> >> root  16806  0.0  0.0  0  0 ?  S  14:58   0:00 [f2fs_gc-8:34]
> >> root  16817  0.0  0.0  0  0 ?  S  14:58   0:00 [f2fs_gc-8:52]
> >>
> >
> > root  16756  0.0  0.0  0  0 ?  S  14:57   0:00 [f2fs_gc-sdb1]
> > root  16765  0.0  0.0  0  0 ?  S  14:57   0:00 [f2fs_gc-sdb2]
> >
> > IMO, it would be better to describe like this.
> > We can simply use bdevname(bdev, name), so if no objection, I'll rebase
> > this patch with this.
> > Please, give me your opinion.
> > Thanks,
> Hi Jaegeuk.
> 
> Although it is good opinion to have user friendly names in the task
> list, but we cannot have such names.
> 
> Because, even though bdevname() will provide the correct string. But
> there is a limitation from the task struct command length.
> The Task struct allows for the name to be maximum of ‘16’ characters in length.
> char comm[TASK_COMM_LEN];
> 
> /* Task command name length */
> #define TASK_COMM_LEN 16
> So, the task name would be truncated to ‘16’ characters.
> 
> In case like for MMC partitions where partition name can be like:
> mmcblk0p18, the name would become f2fs_gc-mmcblk0p18 -> this will be
> truncate to “f2fs_gc-mmcblk0p”

Agreed.
Thank you for explanation. :)

> 
> Let me know your opinion.
> Thanks.
> >
> >
> >> Signed-off-by: Namjae Jeon <namjae.jeon@...sung.com>
> >> Signed-off-by: Amit Sahrawat <a.sahrawat@...sung.com>
> >> ---
> >>  fs/f2fs/gc.c |    3 ++-
> >>  1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >> index 742135a..b0c1f8c 100644
> >> --- a/fs/f2fs/gc.c
> >> +++ b/fs/f2fs/gc.c
> >> @@ -91,6 +91,7 @@ static int gc_thread_func(void *data)
> >>  int start_gc_thread(struct f2fs_sb_info *sbi)
> >>  {
> >>  	struct f2fs_gc_kthread *gc_th;
> >> +	dev_t dev = sbi->sb->s_bdev->bd_dev;
> >>
> >>  	if (!test_opt(sbi, BG_GC))
> >>  		return 0;
> >> @@ -101,7 +102,7 @@ int start_gc_thread(struct f2fs_sb_info *sbi)
> >>  	sbi->gc_thread = gc_th;
> >>  	init_waitqueue_head(&sbi->gc_thread->gc_wait_queue_head);
> >>  	sbi->gc_thread->f2fs_gc_task = kthread_run(gc_thread_func, sbi,
> >> -				"f2fs_gc-%s", dev_name(sbi->sb->s_bdi->dev));
> >> +				"f2fs_gc-%u:%u", MAJOR(dev), MINOR(dev));
> >>  	if (IS_ERR(gc_th->f2fs_gc_task)) {
> >>  		kfree(gc_th);
> >>  		sbi->gc_thread = NULL;
> >
> > --
> > Jaegeuk Kim
> > Samsung
> >
> --
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-- 
Jaegeuk Kim
Samsung

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