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. -- chandan
