On 14 May 2012 07:12, Namhyung Kim <namhyung.kim@xxxxxxx> wrote: > Hi, > > On Fri, 11 May 2012 20:32:56 +0530, Saugata Das wrote: >> From: Saugata Das <saugata.das@xxxxxxxxxx> >> >> Today, storage devices like eMMC has special features like data tagging >> (introduced in MMC-4.5 version) in order to improve performance of some >> specific writes. On MMC stack, data tagging is used for all writes which >> has REQ_META flag set. This patch adds the capability to add REQ_META flag >> during meta data write. >> > > AFAIK, the REQ_META is only for marking a bio/req to be recognized when > using blktrace or something. You can use REQ_PRIO for the purpose but it > applies only if your ioscheduler is CFQ. > > But I'm not aware how the MMC stack works, so I might be missing something. > Today on ext4, REQ_META or REQ_PRIO are only used during read operation. For meta-data writes, no special flag (REQ_META or REQ_PRIO) is set. On eMMC, we depend on REQ_META flag to implement the "reliable write" and "data tag" feature, which are linked with additional reliability and performance for file system meta-data writes. > Thanks, > Namhyung > > >> Signed-off-by: Saugata Das <saugata.das@xxxxxxxxxx> >> --- >> fs/buffer.c | 10 ++++++++-- >> include/linux/buffer_head.h | 2 ++ >> 2 files changed, 10 insertions(+), 2 deletions(-) >> >> diff --git a/fs/buffer.c b/fs/buffer.c >> index 36d6665..688b38b 100644 >> --- a/fs/buffer.c >> +++ b/fs/buffer.c >> @@ -1685,7 +1685,10 @@ static int __block_write_full_page(struct inode *inode, struct page *page, >> do { >> struct buffer_head *next = bh->b_this_page; >> if (buffer_async_write(bh)) { >> - submit_bh(write_op, bh); >> + if (buffer_meta(bh)) >> + submit_bh(write_op | REQ_META, bh); >> + else >> + submit_bh(write_op, bh); >> nr_underway++; >> } >> bh = next; >> @@ -1739,7 +1742,10 @@ recover: >> struct buffer_head *next = bh->b_this_page; >> if (buffer_async_write(bh)) { >> clear_buffer_dirty(bh); >> - submit_bh(write_op, bh); >> + if (buffer_meta(bh)) >> + submit_bh(write_op | REQ_META, bh); >> + else >> + submit_bh(write_op, bh); >> nr_underway++; >> } >> bh = next; >> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h >> index ef26043..0776564 100644 >> --- a/include/linux/buffer_head.h >> +++ b/include/linux/buffer_head.h >> @@ -34,6 +34,7 @@ enum bh_state_bits { >> BH_Write_EIO, /* I/O error on write */ >> BH_Unwritten, /* Buffer is allocated on disk but not written */ >> BH_Quiet, /* Buffer Error Prinks to be quiet */ >> + BH_Meta, /* Is meta */ >> >> BH_PrivateStart,/* not a state bit, but the first bit available >> * for private allocation by other entities >> @@ -126,6 +127,7 @@ BUFFER_FNS(Delay, delay) >> BUFFER_FNS(Boundary, boundary) >> BUFFER_FNS(Write_EIO, write_io_error) >> BUFFER_FNS(Unwritten, unwritten) >> +BUFFER_FNS(Meta, meta) >> >> #define bh_offset(bh) ((unsigned long)(bh)->b_data & ~PAGE_MASK) >> #define touch_buffer(bh) mark_page_accessed(bh->b_page) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html