Re: [f2fs-dev] [PATCH v3] f2fs: fix performance issue observed with multi-thread sequential read

[Jaegeuk Kim]

On 08/13, Chao Yu wrote:
> Hi Jaegeuk,
> 
> On 2018/8/11 2:56, Jaegeuk Kim wrote:
> > This reverts the commit - "b93f771 - f2fs: remove writepages lock"
> > to fix the drop in sequential read throughput.
> > 
> > Test: ./tiotest -t 32 -d /data/tio_tmp -f 32 -b 524288 -k 1 -k 3 -L
> > device: UFS
> > 
> > Before -
> > read throughput: 185 MB/s
> > total read requests: 85177 (of these ~80000 are 4KB size requests).
> > total write requests: 2546 (of these ~2208 requests are written in 512KB).
> > 
> > After -
> > read throughput: 758 MB/s
> > total read requests: 2417 (of these ~2042 are 512KB reads).
> > total write requests: 2701 (of these ~2034 requests are written in 512KB).
> 
> IMO, it only impact sequential read performance in a large file which may be
> fragmented during multi-thread writing.
> 
> In android environment, mostly, the large file should be cold type, such as apk,
> mp3, rmvb, jpeg..., so I think we only need to serialize writepages() for cold
> data area writer.
> 
> So how about adding a mount option to serialize writepage() for different type
> of log, e.g. in android, using serialize=4; by default, using serialize=7
> HOT_DATA	1
> WARM_DATA	2
> COLD_DATA	4

Well, I don't think we need to give too many mount options for this fragmented
case. How about doing this for the large files only like this?