Commit 6188e877 authored by Andreas Gruenbacher's avatar Andreas Gruenbacher
Browse files

gfs2: Some documentation updates 



The calc_reserved description claims that buf_limit is 502 (on 4k
filesystems), but it is actually 503.  Fix / clarify the entire
description.

Signed-off-by: default avatarAndreas Gruenbacher <agruenba@redhat.com>
parent 5a4e9c60

fs/gfs2/log.c

+11 −13
Original line number Diff line number Diff line
@@ -50,10 +50,12 @@ unsigned int gfs2_struct2blk(struct gfs2_sbd *sdp, unsigned int nstruct) 
	unsigned int blks;

	unsigned int first, second;



	/* The initial struct gfs2_log_descriptor block */

	blks = 1;

	first = sdp->sd_ldptrs;



	if (nstruct > first) {

		/* Subsequent struct gfs2_meta_header blocks */

		second = sdp->sd_inptrs;

		blks += DIV_ROUND_UP(nstruct - first, second);

	}
@@ -507,24 +509,20 @@ static inline unsigned int log_distance(struct gfs2_sbd *sdp, unsigned int newer 
}



/**

 * calc_reserved - Calculate the number of blocks to reserve when

 *                 refunding a transaction's unused buffers.

 * calc_reserved - Calculate the number of blocks to keep reserved

 * @sdp: The GFS2 superblock

 *

 * This is complex.  We need to reserve room for all our currently used

 * metadata buffers (e.g. normal file I/O rewriting file time stamps) and 

 * all our journaled data buffers for journaled files (e.g. files in the 

 * metadata blocks (e.g. normal file I/O rewriting file time stamps) and

 * all our journaled data blocks for journaled files (e.g. files in the

 * meta_fs like rindex, or files for which chattr +j was done.)

 * If we don't reserve enough space, gfs2_log_refund and gfs2_log_flush

 * will count it as free space (sd_log_blks_free) and corruption will follow.

 * If we don't reserve enough space, corruption will follow.

 *

 * We can have metadata bufs and jdata bufs in the same journal.  So each

 * type gets its own log header, for which we need to reserve a block.

 * In fact, each type has the potential for needing more than one header 

 * in cases where we have more buffers than will fit on a journal page.

 * We can have metadata blocks and jdata blocks in the same journal.  Each

 * type gets its own log descriptor, for which we need to reserve a block.

 * In fact, each type has the potential for needing more than one log descriptor

 * in cases where we have more blocks than will fit in a log descriptor.

 * Metadata journal entries take up half the space of journaled buffer entries.

 * Thus, metadata entries have buf_limit (502) and journaled buffers have

 * databuf_limit (251) before they cause a wrap around.

 *

 * Also, we need to reserve blocks for revoke journal entries and one for an

 * overall header for the lot.