On Tue, Nov 18, 2008 at 1:06 AM, Ruby <ruby185@xxxxxxxxx> wrote:
> hi, all
>
> as I understand, ->readpage() will be invoked on address space object at
> some point when you do a syscall on read.
> for ext3, it will be ext3_readpage, which ask mpage_readpage() to do the
> job.
>
> what I don't follow is why the function doc right before mapge_readpage()
> claims "This isn't called much at all".
>
These are the caller I can find:
./fs/gfs2/ops_address.c:
error = mpage_readpage(page, gfs2_block_map);
* 3. mpage_readpages() does most of the heavy lifting in the common case.
ret = mpage_readpages(mapping, pages, nr_pages, gfs2_block_map);
./fs/ocfs2/aops.c:
err = mpage_readpages(mapping, pages, nr_pages, ocfs2_get_block);
./fs/ext3/inode.c:
return mpage_readpage(page, ext3_get_block);
return mpage_readpages(mapping, pages, nr_pages, ext3_get_block);
./fs/ext4/inode.c:
return mpage_readpage(page, ext4_get_block);
return mpage_readpages(mapping, pages, nr_pages, ext4_get_block);
./fs/omfs/file.c:
return mpage_readpages(mapping, pages, nr_pages, omfs_get_block);
./fs/ext2/inode.c:
return mpage_readpage(page, ext2_get_block);
return mpage_readpages(mapping, pages, nr_pages, ext2_get_block);
./fs/reiserfs/inode.c:
return mpage_readpages(mapping, pages, nr_pages, reiserfs_get_block);
./fs/xfs/linux-2.6/xfs_aops.c:
return mpage_readpage(page, xfs_get_blocks);
return mpage_readpages(mapping, pages, nr_pages, xfs_get_blocks);
./fs/fat/inode.c:
return mpage_readpage(page, fat_get_block);
return mpage_readpages(mapping, pages, nr_pages, fat_get_block);
./fs/jfs/inode.c:
return mpage_readpage(page, jfs_get_block);
return mpage_readpages(mapping, pages, nr_pages, jfs_get_block);
So for ext3, the caller is ext3_readpage(), since ext3_readpages()
called mpage_readpages(). Doing an ftrace based on "gedit" usage:
+ cat /debug/tracing/trace
# tracer: function
#
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |
ping-16862 [001] 4154504124.726653: ext3_readpages
<-__do_page_cache_readahead
ping-16862 [001] 4154504124.734300: ext3_readpages
<-__do_page_cache_readahead
ping-16862 [001] 4154504130.842834: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504132.875053: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504132.875279: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504132.875635: ext3_readpages
<-__do_page_cache_readahead
sleep-16871 [000] 4154504132.876264: ext3_readpages
<-__do_page_cache_readahead
sleep-16871 [000] 4154504132.975226: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.518396: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.542090: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.554723: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.561582: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.568196: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.571578: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.573920: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.583903: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.587428: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.597227: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.598789: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.600786: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.601692: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.605248: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.607422: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.652960: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.672707: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.682435: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.696935: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.736472: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.745688: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.757596: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.787324: ext3_readpages
<-__do_page_cache_readahead
gedit-16870 [001] 4154504133.794610: ext3_readpages
<-__do_page_cache_readahead
We can see majority are using ext3_readpages(), not ext3_readpage().
So I guessed that's what it meant - "pages" are more often used than
"page". And they don't overlap.
> is this not on the primary read I/O path anymore?
>
>
> thanks
>
> Ruby
>
--
Regards,
Peter Teoh
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