Re: [f2fs-dev] [PATCH v2] f2fs: readahead node blocks in F2FS_GET_BLOCK_PRECACHE mode

["Yunji Kang" <yunji0.kang@samsung.com>]

> > In f2fs_precache_extents(), For large files, It requires reading many
> > node blocks. Instead of reading each node block with synchronous I/O,
> > this patch applies readahead so that node blocks can be fetched in
> > advance.
> >
> > It reduces the overhead of repeated sync reads and improves efficiency
> > when precaching extents of large files.
> >
> > I created a file with the same largest extent and executed the test.
> > For this experiment, I set the file's largest extent with an offset of
> > 0 and a size of 1GB. I configured the remaining area with 100MB extents.
> >
> > 5GB test file:
> > dd if=/dev/urandom of=test1 bs=1m count=5120 cp test1 test2 fsync
> > test1 dd if=test1 of=test2 bs=1m skip=1024 seek=1024 count=100
> > conv=notrunc dd if=test1 of=test2 bs=1m skip=1224 seek=1224 count=100
> > conv=notrunc ...
> > dd if=test1 of=test2 bs=1m skip=5024 seek=5024 count=100 conv=notrunc
> > reboot
> >
> > I also created 10GB and 20GB files with large extents using the same
> > method.
> >
> > ioctl(F2FS_IOC_PRECACHE_EXTENTS) test results are as follows:
> >   +-----------+---------+---------+-----------+
> >   | File size | Before  | After   | Reduction |
> >   +-----------+---------+---------+-----------+
> >   | 5GB       | 101.8ms | 72.1ms  | 29.2%     |
> >   | 10GB      | 222.9ms | 149.5ms | 32.9%     |
> >   | 20GB      | 446.2ms | 276.3ms | 38.1%     |
> >   +-----------+---------+---------+-----------+
> 
> Yunji,
> 
> Will we gain better performance if we readahead more node pages w/
> sychronous request for precache extent case? Have you tried that?
> 
> Thanks,
> 

Does “readahead more node pages” mean removing this condition?
" offset[i - 1] % MAX_RA_NODE == 0 "

I originally added the condition to prevent unnecessary readahead requests, 
but it seems this condition was actually blocking valid readahead as well.

After removing the condition and running tests, 
I confirmed that more readahead node pages are being issued.

I’ll share the test results along with the improved patch.

Thanks,

> > Tested on a 256GB mobile device with an SM8750 chipset.
> >
> > Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
> > Reviewed-by: Sunmin Jeong <s_min.jeong@samsung.com>
> > Signed-off-by: Yunji Kang <yunji0.kang@samsung.com>
> > ---
> > v2:
> >  - Modify the readahead condition check routine for better code
> > readability.
> >  - Update the title from 'node block' to 'node blocks'.
> >
> >  fs/f2fs/data.c | 3 +++
> >  fs/f2fs/f2fs.h | 1 +
> >  fs/f2fs/node.c | 5 ++++-
> >  3 files changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c index
> > 7961e0ddfca3..ab3117e3b24a 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -1572,6 +1572,9 @@ int f2fs_map_blocks(struct inode *inode, struct
> f2fs_map_blocks *map, int flag)
> >  	pgofs =	(pgoff_t)map->m_lblk;
> >  	end = pgofs + maxblocks;
> >
> > +	if (flag == F2FS_GET_BLOCK_PRECACHE)
> > +		mode = LOOKUP_NODE_PRECACHE;
> > +
> >  next_dnode:
> >  	if (map->m_may_create) {
> >  		if (f2fs_lfs_mode(sbi))
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h index
> > 9d3bc9633c1d..3ce41528d48e 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -651,6 +651,7 @@ enum {
> >  					 * look up a node with readahead called
> >  					 * by get_data_block.
> >  					 */
> > +	LOOKUP_NODE_PRECACHE,		/* look up a node for
> F2FS_GET_BLOCK_PRECACHE */
> >  };
> >
> >  #define DEFAULT_RETRY_IO_COUNT	8	/* maximum retry read IO or flush
> count */
> > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c index
> > 4254db453b2d..d4bf3ce715c5 100644
> > --- a/fs/f2fs/node.c
> > +++ b/fs/f2fs/node.c
> > @@ -860,7 +860,10 @@ int f2fs_get_dnode_of_data(struct dnode_of_data *dn,
> pgoff_t index, int mode)
> >  			set_nid(parent, offset[i - 1], nids[i], i == 1);
> >  			f2fs_alloc_nid_done(sbi, nids[i]);
> >  			done = true;
> > -		} else if (mode == LOOKUP_NODE_RA && i == level && level > 1)
> {
> > +		} else if ((i == level && level > 1) &&
> > +				(mode == LOOKUP_NODE_RA ||
> > +				(mode == LOOKUP_NODE_PRECACHE &&
> > +				offset[i - 1] % MAX_RA_NODE == 0))) {
> >  			nfolio[i] = f2fs_get_node_folio_ra(parent, offset[i -
> 1]);
> >  			if (IS_ERR(nfolio[i])) {
> >  				err = PTR_ERR(nfolio[i]);





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