Messages in this thread | | | Date | Tue, 30 Jun 2020 13:43:48 -0700 | From | Nathan Chancellor <> | Subject | Re: [f2fs-dev] [PATCH v3] f2fs: avoid readahead race condition |
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On Mon, Jun 29, 2020 at 01:27:20PM -0700, Jaegeuk Kim wrote: > If two readahead threads having same offset enter in readpages, every read > IOs are split and issued to the disk which giving lower bandwidth. > > This patch tries to avoid redundant readahead calls. > > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org> > --- > v3: > - use READ|WRITE_ONCE > v2: > - add missing code to bypass read > > fs/f2fs/data.c | 18 ++++++++++++++++++ > fs/f2fs/f2fs.h | 1 + > fs/f2fs/super.c | 2 ++ > 3 files changed, 21 insertions(+) > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c > index 995cf78b23c5e..360b4c9080d97 100644 > --- a/fs/f2fs/data.c > +++ b/fs/f2fs/data.c > @@ -2296,6 +2296,7 @@ static int f2fs_mpage_readpages(struct inode *inode, > unsigned nr_pages = rac ? readahead_count(rac) : 1; > unsigned max_nr_pages = nr_pages; > int ret = 0; > + bool drop_ra = false; > > map.m_pblk = 0; > map.m_lblk = 0; > @@ -2306,10 +2307,24 @@ static int f2fs_mpage_readpages(struct inode *inode, > map.m_seg_type = NO_CHECK_TYPE; > map.m_may_create = false; > > + /* > + * Two readahead threads for same address range can cause race condition > + * which fragments sequential read IOs. So let's avoid each other. > + */ > + if (rac && readahead_count(rac)) { > + if (READ_ONCE(F2FS_I(inode)->ra_offset) == readahead_index(rac)) > + drop_ra = true; > + else > + WRITE_ONCE(F2FS_I(inode)->ra_offset, > + readahead_index(rac)); > + } > + > for (; nr_pages; nr_pages--) { > if (rac) { > page = readahead_page(rac); > prefetchw(&page->flags); > + if (drop_ra) > + goto next_page;
When CONFIG_F2FS_FS_COMPRESSION is not set (i.e. x86_64 defconfig + CONFIG_F2FS_FS=y):
$ make -skj"$(nproc)" O=out distclean defconfig fs/f2fs/data.o ../fs/f2fs/data.c: In function ‘f2fs_mpage_readpages’: ../fs/f2fs/data.c:2327:5: error: label ‘next_page’ used but not defined 2327 | goto next_page; | ^~~~ ...
Cheers, Nathan
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