On 09/17, Chao Yu wrote: > On 2019/9/16 23:37, Jaegeuk Kim wrote: > > On 09/16, Chao Yu wrote: > >> On 2019/9/9 20:04, Jaegeuk Kim wrote: > >>> On 09/09, Chao Yu wrote: > >>>> On 2019/9/9 16:06, Jaegeuk Kim wrote: > >>>>> On 09/09, Chao Yu wrote: > >>>>>> On 2019/9/9 9:25, Jaegeuk Kim wrote: > >>>>>>> GC must avoid select the same victim again. > >>>>>> > >>>>>> Blocks in previous victim will occupy addition free segment, I doubt > >>>>>> after this > >>>>>> change, FGGC may encounter out-of-free space issue more frequently. > >>>>> > >>>>> Hmm, actually this change seems wrong by sec_usage_check(). > >>>>> We may be able to avoid this only in the suspicious loop? > >>>>> > >>>>> --- > >>>>> fs/f2fs/gc.c | 2 +- > >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) > >>>>> > >>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c > >>>>> index e88f98ddf396..5877bd729689 100644 > >>>>> --- a/fs/f2fs/gc.c > >>>>> +++ b/fs/f2fs/gc.c > >>>>> @@ -1326,7 +1326,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, > >>>>> round++; > >>>>> } > >>>>> > >>>>> - if (gc_type == FG_GC) > >>>>> + if (gc_type == FG_GC && seg_freed) > >>>> > >>>> That's original solution Sahitya provided to avoid infinite loop of GC, > >>>> but I > >>>> suggest to find the root cause first, then we added .invalid_segmap for > >>>> that > >>>> purpose. > >>> > >>> I've checked the Sahitya's patch. So, it seems the problem can happen due > >>> to > >>> is_alive or atomic_file. > >> > >> For some conditions, this doesn't help, for example, two sections contain > >> the > >> same fewest valid blocks, it will cause to loop selecting them if it fails > >> to > >> migrate blocks. > >> > >> How about keeping it as it is to find potential bug. > > > > I think it'd be fine to merge this. Could you check the above scenario in > > more > > detail? > > I haven't saw this in real scenario yet. > > What I mean is if there is a bug (maybe in is_alive()) failing us to GC on one > section, when that bug happens in two candidates, there could be the same > condition that GC will run into loop (select A, fail to migrate; select B, > fail > to migrate, select A...). > > But I guess the benefit of this change is, if FGGC fails to migrate block due > to > i_gc_rwsem race, selecting another section and later retrying previous one may > avoid lock race, right?
In any case, I think this can avoid potenial GC loop. At least to me, it'd be quite risky, if we remain this just for debugging purpose only. > > Thanks, > > > > > Thanks, > > > >> > >> Thanks, > >> > >>> > >>>> > >>>> Thanks, > >>>> > >>>>> sbi->cur_victim_sec = NULL_SEGNO; > >>>>> > >>>>> if (sync) > >>>>> > >>> . > >>> > > . > >
