On 2017/1/5 7:44, Jaegeuk Kim wrote: > On 01/04, Chao Yu wrote: >> Hi Jaegeuk, >> >> On 2016/12/31 2:51, Jaegeuk Kim wrote: >>> This patch implements IO alignment by filling dummy blocks in DATA and NODE >>> write bios. If we can guarantee, for example, 32KB or 64KB for such the IOs, >>> we can eliminate underlying dummy page problem which FTL conducts in order to >>> close MLC or TLC partial written pages. >>> >>> Note that, >>> - it requires "-o mode=lfs". >>> - IO size should be power of 2, not exceed BIO_MAX_PAGES, 256. >>> - read IO is still 4KB. >>> - do checkpoint at fsync, if dummy NODE page was written. >> >> Which scenario we can benefit from? Any numbers? > > I described it in the patch. This is not targetting for performance improvement > for now, but to address the dummy page write problem in FTL so that we can later > implement very simple host-level FTL on top of open-channel SSD. Alright, if we are doing this since FTL implementation is moved up, so I can understand that. Thanks, > >> I doubt that there are some potential side-effect points: >> - write amplification will be more serious than before >> - free space will be more fragmented since dummy blocks is separated in whole >> address space >> - there is less chance to merge small(unaligned) IOs in block layer > > I agree, so I just added this as a mount option experimentally. > One point would be that, if f2fs doesn't do this, FTL should do it. So I think, > from the system point of view, f2fs is a better layer to do it. > > Thanks, > >> >> Thoughts? >> >> Thanks, > > . > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
