From: Leonardo Bras <leobras.c@gmail.com>
To: Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Andrew Morton <akpm@linux-foundation.org>,
Leonardo Bras <leobras.c@gmail.com>,
Sandipan Das <sandipan@linux.ibm.com>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
Logan Gunthorpe <logang@deltatee.com>,
Mike Rapoport <rppt@kernel.org>,
Bharata B Rao <bharata@linux.ibm.com>,
Dan Williams <dan.j.williams@intel.com>,
Nicholas Piggin <npiggin@gmail.com>,
Nathan Lynch <nathanl@linux.ibm.com>,
David Hildenbrand <david@redhat.com>,
Laurent Dufour <ldufour@linux.ibm.com>,
Scott Cheloha <cheloha@linux.ibm.com>,
David Gibson <david@gibson.dropbear.id.au>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: [PATCH 1/3] powerpc/mm/hash: Avoid resizing-down HPT on first memory hotplug
Date: Fri, 12 Mar 2021 04:29:39 -0300 [thread overview]
Message-ID: <20210312072940.598696-2-leobras.c@gmail.com> (raw)
In-Reply-To: <20210312072940.598696-1-leobras.c@gmail.com>
Because hypervisors may need to create HPTs without knowing the guest
page size, the smallest used page-size (4k) may be chosen, resulting in
a HPT that is possibly bigger than needed.
On a guest with bigger page-sizes, the amount of entries for HTP may be
too high, causing the guest to ask for a HPT resize-down on the first
hotplug.
This becomes a problem when HPT resize-down fails, and causes the
HPT resize to be performed on every LMB added, until HPT size is
compatible to guest memory size, causing a major slowdown.
So, avoiding HPT resizing-down on hot-add significantly improves memory
hotplug times.
As an example, hotplugging 256GB on a 129GB guest took 710s without this
patch, and 21s after applied.
Signed-off-by: Leonardo Bras <leobras.c@gmail.com>
---
arch/powerpc/mm/book3s64/hash_utils.c | 36 ++++++++++++++++-----------
1 file changed, 21 insertions(+), 15 deletions(-)
diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index 73b06adb6eeb..cfb3ec164f56 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -794,7 +794,7 @@ static unsigned long __init htab_get_table_size(void)
}
#ifdef CONFIG_MEMORY_HOTPLUG
-static int resize_hpt_for_hotplug(unsigned long new_mem_size)
+static int resize_hpt_for_hotplug(unsigned long new_mem_size, bool shrinking)
{
unsigned target_hpt_shift;
@@ -803,19 +803,25 @@ static int resize_hpt_for_hotplug(unsigned long new_mem_size)
target_hpt_shift = htab_shift_for_mem_size(new_mem_size);
- /*
- * To avoid lots of HPT resizes if memory size is fluctuating
- * across a boundary, we deliberately have some hysterisis
- * here: we immediately increase the HPT size if the target
- * shift exceeds the current shift, but we won't attempt to
- * reduce unless the target shift is at least 2 below the
- * current shift
- */
- if (target_hpt_shift > ppc64_pft_size ||
- target_hpt_shift < ppc64_pft_size - 1)
- return mmu_hash_ops.resize_hpt(target_hpt_shift);
+ if (shrinking) {
- return 0;
+ /*
+ * To avoid lots of HPT resizes if memory size is fluctuating
+ * across a boundary, we deliberately have some hysterisis
+ * here: we immediately increase the HPT size if the target
+ * shift exceeds the current shift, but we won't attempt to
+ * reduce unless the target shift is at least 2 below the
+ * current shift
+ */
+
+ if (target_hpt_shift >= ppc64_pft_size - 1)
+ return 0;
+
+ } else if (target_hpt_shift <= ppc64_pft_size) {
+ return 0;
+ }
+
+ return mmu_hash_ops.resize_hpt(target_hpt_shift);
}
int hash__create_section_mapping(unsigned long start, unsigned long end,
@@ -828,7 +834,7 @@ int hash__create_section_mapping(unsigned long start, unsigned long end,
return -1;
}
- resize_hpt_for_hotplug(memblock_phys_mem_size());
+ resize_hpt_for_hotplug(memblock_phys_mem_size(), false);
rc = htab_bolt_mapping(start, end, __pa(start),
pgprot_val(prot), mmu_linear_psize,
@@ -847,7 +853,7 @@ int hash__remove_section_mapping(unsigned long start, unsigned long end)
int rc = htab_remove_mapping(start, end, mmu_linear_psize,
mmu_kernel_ssize);
- if (resize_hpt_for_hotplug(memblock_phys_mem_size()) == -ENOSPC)
+ if (resize_hpt_for_hotplug(memblock_phys_mem_size(), true) == -ENOSPC)
pr_warn("Hash collision while resizing HPT\n");
return rc;
--
2.29.2
next prev parent reply other threads:[~2021-03-12 7:32 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-12 7:29 [PATCH 0/3] powerpc/mm/hash: Time improvements for memory hot(un)plug Leonardo Bras
2021-03-12 7:29 ` Leonardo Bras [this message]
2021-03-22 6:49 ` [PATCH 1/3] powerpc/mm/hash: Avoid resizing-down HPT on first memory hotplug David Gibson
2021-04-09 2:16 ` Leonardo Bras
2021-03-12 7:29 ` [PATCH 2/3] powerpc/mm/hash: Avoid multiple HPT resize-ups on " Leonardo Bras
2021-03-22 7:55 ` David Gibson
2021-04-09 2:51 ` Leonardo Bras
2021-04-19 5:34 ` David Gibson
2021-03-12 7:29 ` [PATCH 3/3] powerpc/mm/hash: Avoid multiple HPT resize-downs on memory hotunplug Leonardo Bras
2021-03-22 23:45 ` David Gibson
2021-04-09 3:31 ` Leonardo Bras
2021-04-19 5:37 ` David Gibson
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