From b445b25b273d263f032fadd717e5731185b74bf5 Mon Sep 17 00:00:00 2001 From: shodanshok Date: Fri, 11 Nov 2022 19:41:36 +0100 Subject: [PATCH] Fix arc_p aggressive increase The original ARC paper called for an initial 50/50 MRU/MFU split and this is accounted in various places where arc_p = arc_c >> 1, with further adjustment based on ghost lists size/hit. However, in current code both arc_adapt() and arc_get_data_impl() aggressively grow arc_p until arc_c is reached, causing unneeded pressure on MFU and greatly reducing its scan-resistance until ghost list adjustments kick in. This patch restores the original behavior of initially having arc_p as 1/2 of total ARC, without preventing MRU to use up to 100% total ARC when MFU is empty. Reviewed-by: Alexander Motin Reviewed-by: Brian Behlendorf Signed-off-by: Gionatan Danti Closes #14137 Closes #14120 --- module/zfs/arc.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/module/zfs/arc.c b/module/zfs/arc.c index 1f97631f9..f51f427c1 100644 --- a/module/zfs/arc.c +++ b/module/zfs/arc.c @@ -5173,7 +5173,7 @@ arc_adapt(int bytes, arc_state_t *state) atomic_add_64(&arc_c, (int64_t)bytes); if (arc_c > arc_c_max) arc_c = arc_c_max; - else if (state == arc_anon) + else if (state == arc_anon && arc_p < arc_c >> 1) atomic_add_64(&arc_p, (int64_t)bytes); if (arc_p > arc_c) arc_p = arc_c; @@ -5386,7 +5386,8 @@ arc_get_data_impl(arc_buf_hdr_t *hdr, uint64_t size, const void *tag, if (aggsum_upper_bound(&arc_sums.arcstat_size) < arc_c && hdr->b_l1hdr.b_state == arc_anon && (zfs_refcount_count(&arc_anon->arcs_size) + - zfs_refcount_count(&arc_mru->arcs_size) > arc_p)) + zfs_refcount_count(&arc_mru->arcs_size) > arc_p && + arc_p < arc_c >> 1)) arc_p = MIN(arc_c, arc_p + size); } }