On Thu, Dec 23, 2021 at 11:36:15AM +0530, Chandan Babu R wrote: > On 10 Nov 2021 at 07:28, Darrick J. Wong wrote: > > From: Darrick J. Wong <djwong@xxxxxxxxxx> > > > > Wengang Wang was trying to work through a buffer log item by consulting > > the ondisk format documentation, and was confused by the formula given > > in section 14.3.14 regarding the size of blf_data_map, aka the dirty > > bitmap for buffer log items. We noticed that the documentation doesn't > > match what the kernel actually does, so let's fix this. > > > > Reported-by: Wengang Wang <wen.gang.wang@xxxxxxxxxx> > > Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx> > > --- > > .../journaling_log.asciidoc | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/design/XFS_Filesystem_Structure/journaling_log.asciidoc b/design/XFS_Filesystem_Structure/journaling_log.asciidoc > > index 1dba56e..894d3e5 100644 > > --- a/design/XFS_Filesystem_Structure/journaling_log.asciidoc > > +++ b/design/XFS_Filesystem_Structure/journaling_log.asciidoc > > @@ -992,7 +992,7 @@ The size of +blf_data_map+, in 32-bit words. > > This variable-sized array acts as a dirty bitmap for the logged buffer. Each > > 1 bit represents a dirty region in the buffer, and each run of 1 bits > > corresponds to a subsequent log item containing the new contents of the buffer > > -area. Each bit represents +(blf_len * 512) / (blf_map_size * NBBY)+ bytes. > > +area. Each bit represents +(blf_len * 512) / (blf_map_size * sizeof(unsigned int) * NBBY)+ bytes. > > > > [[Buffer_Data_Log_Item]] > > === Buffer Data Log Item > > The calculation looks correct. However, wouldn't it be better to mention, > > "Each bit represents XFS_BLF_CHUNK (i.e. 128) bytes" > > ... or some such variant involving XFS_BLF_CHUNK. Ok. --D > > -- > chandan
