From 4c0cfebdf3c34c9cd2c55844f549fa46b1da3164 Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Thu, 8 Jun 2023 10:39:35 -0400 Subject: ext4: clean up mballoc criteria comments Line wrap and slightly clarify the comments describing mballoc's cirtiera. Define EXT4_MB_NUM_CRS as part of the enum, so that it will automatically get updated when criteria is added or removed. Also fix a potential unitialized use of 'cr' variable if CONFIG_EXT4_DEBUG is enabled. Signed-off-by: Theodore Ts'o --- fs/ext4/ext4.h | 45 +++++++++++++++++++++++++-------------------- fs/ext4/mballoc.c | 19 +++++++++---------- 2 files changed, 34 insertions(+), 30 deletions(-) (limited to 'fs') diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 6a1f013d23f7..45a531446ea2 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -128,47 +128,52 @@ enum SHIFT_DIRECTION { }; /* - * Number of criterias defined. For each criteria, mballoc has slightly - * different way of finding the required blocks nad usually, higher the - * criteria the slower the allocation. We start at lower criterias and keep - * falling back to higher ones if we are not able to find any blocks. - */ -#define EXT4_MB_NUM_CRS 5 -/* - * All possible allocation criterias for mballoc. Lower are faster. + * For each criteria, mballoc has slightly different way of finding + * the required blocks nad usually, higher the criteria the slower the + * allocation. We start at lower criterias and keep falling back to + * higher ones if we are not able to find any blocks. Lower (earlier) + * criteria are faster. */ enum criteria { /* - * Used when number of blocks needed is a power of 2. This doesn't - * trigger any disk IO except prefetch and is the fastest criteria. + * Used when number of blocks needed is a power of 2. This + * doesn't trigger any disk IO except prefetch and is the + * fastest criteria. */ CR_POWER2_ALIGNED, /* - * Tries to lookup in-memory data structures to find the most suitable - * group that satisfies goal request. No disk IO except block prefetch. + * Tries to lookup in-memory data structures to find the most + * suitable group that satisfies goal request. No disk IO + * except block prefetch. */ CR_GOAL_LEN_FAST, /* - * Same as CR_GOAL_LEN_FAST but is allowed to reduce the goal length to - * the best available length for faster allocation. + * Same as CR_GOAL_LEN_FAST but is allowed to reduce the goal + * length to the best available length for faster allocation. */ CR_BEST_AVAIL_LEN, /* - * Reads each block group sequentially, performing disk IO if necessary, to - * find find_suitable block group. Tries to allocate goal length but might trim - * the request if nothing is found after enough tries. + * Reads each block group sequentially, performing disk IO if + * necessary, to find find_suitable block group. Tries to + * allocate goal length but might trim the request if nothing + * is found after enough tries. */ CR_GOAL_LEN_SLOW, /* - * Finds the first free set of blocks and allocates those. This is only - * used in rare cases when CR_GOAL_LEN_SLOW also fails to allocate - * anything. + * Finds the first free set of blocks and allocates + * those. This is only used in rare cases when + * CR_GOAL_LEN_SLOW also fails to allocate anything. */ CR_ANY_FREE, + + /* + * Number of criterias defined. + */ + EXT4_MB_NUM_CRS }; /* criteria below which we use fast block scanning and avoid unnecessary IO */ diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 74ebe31f8d0f..a2475b8c9fb5 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -1035,11 +1035,9 @@ static void ext4_mb_choose_next_group_best_avail(struct ext4_allocation_context if (num_stripe_clusters > 0) { /* - * Try to round up the adjusted goal to stripe size - * (in cluster units) multiple for efficiency. - * - * XXX: Is s->stripe always a power of 2? In that case - * we can use the faster round_up() variant. + * Try to round up the adjusted goal length to + * stripe size (in cluster units) multiple for + * efficiency. */ ac->ac_g_ex.fe_len = roundup(ac->ac_g_ex.fe_len, num_stripe_clusters); @@ -2758,7 +2756,7 @@ static noinline_for_stack int ext4_mb_regular_allocator(struct ext4_allocation_context *ac) { ext4_group_t prefetch_grp = 0, ngroups, group, i; - enum criteria cr, new_cr; + enum criteria new_cr, cr = CR_GOAL_LEN_FAST; int err = 0, first_err = 0; unsigned int nr = 0, prefetch_ios = 0; struct ext4_sb_info *sbi; @@ -2815,12 +2813,13 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) spin_unlock(&sbi->s_md_lock); } - /* Let's just scan groups to find more-less suitable blocks */ - cr = ac->ac_2order ? CR_POWER2_ALIGNED : CR_GOAL_LEN_FAST; /* - * cr == CR_POWER2_ALIGNED try to get exact allocation, - * cr == CR_ANY_FREE try to get anything + * Let's just scan groups to find more-less suitable blocks We + * start with CR_GOAL_LEN_FAST, unless it is power of 2 + * aligned, in which case let's do that faster approach first. */ + if (ac->ac_2order) + cr = CR_POWER2_ALIGNED; repeat: for (; cr < EXT4_MB_NUM_CRS && ac->ac_status == AC_STATUS_CONTINUE; cr++) { ac->ac_criteria = cr; -- cgit v1.2.3