Re: [PATCH] f2fs: add a judgment in add_discard_addrs

[Chao Yu <chao2.yu@samsung.com>]

> -----Original Message-----
> From: He YunLei [mailto:heyunlei@huawei.com]
> Sent: Wednesday, September 09, 2015 7:54 AM
> To: Chao Yu
> Cc: jaegeuk@kernel.org; linux-f2fs-devel@lists.sourceforge.net; bintian.wang@huawei.com
> Subject: Re: [f2fs-dev] [PATCH] f2fs: add a judgment in add_discard_addrs
> 
> On 2015/9/8 19:14, Chao Yu wrote:
> > Hi Yunlei,
> >
> >> -----Original Message-----
> >> From: Yunlei He [mailto:heyunlei@huawei.com]
> >> Sent: Tuesday, September 08, 2015 6:51 PM
> >> To: chao2.yu@samsung.com; jaegeuk@kernel.org; linux-f2fs-devel@lists.sourceforge.net
> >> Cc: bintian.wang@huawei.com; Yunlei He
> >> Subject: [f2fs-dev] [PATCH] f2fs: add a judgment in add_discard_addrs
> >>
> >> CP_DISCARD traverse all segments in fstrim_range to add small discards,
> >> it is better to select entry->len bigger than trim_minlen.
> >
> > If we mount with 'discard' option, f2fs will trigger real-time discard
> > when do checkpoint. If we add judgment condition here, fragmented invalid
> > blocks will not be discarded since we stop adding them in pending list
> > through __add_discard_entry.
> 
> This judgment condition is only valid for cp reason CP_DISCARD, and has no influence
> to other checkpoint. The process of fstrim adds all invalid blocks in pending list and
> deletes entries which len < trim_minlen when issue discard. Can we do the selection
> when added?

__add_discard_entry will try to merge small discards in pending list, and merged discard
may be the eligible candidate, so we'd better not skip that.

Thanks,

> 
> Thanks,
> 
> >
> > Thanks,
> >
> >>
> >> Signed-off-by: Yunlei He <heyunlei@huawei.com>
> >> ---
> >>   fs/f2fs/segment.c | 3 ++-
> >>   1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >> index 78e6d06..a0dab7a 100644
> >> --- a/fs/f2fs/segment.c
> >> +++ b/fs/f2fs/segment.c
> >> @@ -599,7 +599,8 @@ static void add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control
> >> *cpc)
> >>   			break;
> >>
> >>   		end = __find_rev_next_zero_bit(dmap, max_blocks, start + 1);
> >> -		__add_discard_entry(sbi, cpc, se, start, end);
> >> +		if(force && cpc->trim_minlen >= (end - start))
> >> +			__add_discard_entry(sbi, cpc, se, start, end);
> >>   	}
> >>   }
> >>
> >> --
> >> 1.9.1
> >
> >
> >


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