On Tue, Feb 23, 2021 at 10:03:59AM +0800, Huang Jianan wrote: > Hi Xiang, > > On 2021/2/22 12:44, Gao Xiang wrote: > > Hi Jianan, > > > > On Thu, Feb 18, 2021 at 08:00:49PM +0800, Huang Jianan via Linux-erofs > > wrote: > > > From: huangjianan <huangjia...@oppo.com> > > > > > > lz4 uses LZ4_DISTANCE_MAX to record history preservation. When > > > using rolling decompression, a block with a higher compression > > > ratio will cause a larger memory allocation (up to 64k). It may > > > cause a large resource burden in extreme cases on devices with > > > small memory and a large number of concurrent IOs. So appropriately > > > reducing this value can improve performance. > > > > > > Decreasing this value will reduce the compression ratio (except > > > when input_size <LZ4_DISTANCE_MAX). But considering that erofs > > > currently only supports 4k output, reducing this value will not > > > significantly reduce the compression benefits. > > > > > > Signed-off-by: Huang Jianan <huangjia...@oppo.com> > > > Signed-off-by: Guo Weichao <guoweic...@oppo.com> > > > --- > > > fs/erofs/decompressor.c | 13 +++++++++---- > > > fs/erofs/erofs_fs.h | 3 ++- > > > fs/erofs/internal.h | 3 +++ > > > fs/erofs/super.c | 3 +++ > > > 4 files changed, 17 insertions(+), 5 deletions(-) > > > > > > diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c > > > index 1cb1ffd10569..94ae56b3ff71 100644 > > > --- a/fs/erofs/decompressor.c > > > +++ b/fs/erofs/decompressor.c > > > @@ -36,22 +36,27 @@ static int z_erofs_lz4_prepare_destpages(struct > > > z_erofs_decompress_req *rq, > > > struct page *availables[LZ4_MAX_DISTANCE_PAGES] = { NULL }; > > > unsigned long bounced[DIV_ROUND_UP(LZ4_MAX_DISTANCE_PAGES, > > > BITS_PER_LONG)] = { 0 }; > > > + unsigned int lz4_distance_pages = LZ4_MAX_DISTANCE_PAGES; > > > void *kaddr = NULL; > > > unsigned int i, j, top; > > > + if (EROFS_SB(rq->sb)->compr_alg) > > > + lz4_distance_pages = DIV_ROUND_UP(EROFS_SB(rq->sb)->compr_alg, > > > + PAGE_SIZE) + 1; > > > + > > Thanks for your patch, I agree that will reduce runtime memory > > footpoint. and keep max sliding window ondisk in bytes (rather > > than in blocks) is better., but could we calculate lz4_distance_pages > > ahead when reading super_block? > Thanks for suggestion, i will update it soon. > > Also, in the next cycle, I'd like to introduce a bitmap for available > > algorithms (maximum 16-bit) for the next LZMA algorithm, and for each > > available algorithm introduces an on-disk variable-array like below: > > bitmap(16-bit) 2 1 0 > > ... LZMA LZ4 > > __le16 compr_opt_off; /* get the opt array start offset > > (I think also in 4-byte) */ > > > > compr alg 0 (lz4) __le16 alg_opt_size; > > /* next opt off = roundup(off + alg_opt_size, 4); */ > > __le16 lz4_max_distance; > > > > /* 4-byte aligned */ > > compr alg x (if available) u8 alg_opt_size; > > ... > > > > ... > > > > When reading sb, first, it scans the whole bitmap, and get all the > > available algorithms in the image at once. And then read such compr > > opts one-by-one. > > > > Do you have some interest and extra time to implement it? :) That > > makes me work less since I'm debugging mbpcluster compression now... > > Sounds good, I will try to do this part of the work.
Yeah, but it seems to be part of the next LZMA algorithm patchset (with a new brand new INCOMPET feature). I think we could introduce a __le16 lz4_max_distance field from sb reserved for now as a simple backporting solution (since we only use < 64kb sliding window, so the image would be forward compatibility with old kernels. 0 means 64kb sliding window, otherwise it will < 64kb.) And with the new INCOMPAT_COMPR_OPT feature, lz4_max_distance field will be turned into compr_opt_off instead. And variable-array will be used then. So could you revise the patchset as above? Thanks! Thanks, Gao Xiang > > Thanks, > > Jianan > > > Thanks, > > Gao Xiang > > >