linux-kernel - [RFC 1/3] PCI: Equalize hotplug memory for non/occupied slots

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Message-Id: <1531863587-3723-2-git-send-email-jonathan.derrick@intel.com>
Date:   Tue, 17 Jul 2018 15:39:45 -0600
From:   Jon Derrick <jonathan.derrick@...el.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-doc@...r.kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Keith Busch <keith.busch@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Sinan Kaya <okaya@...eaurora.org>,
        Logan Gunthorpe <logang@...tatree.com>,
        Stephen Bates <sbates@...thlin.com>,
        Jon Derrick <jonathan.derrick@...el.com>
Subject: [RFC 1/3] PCI: Equalize hotplug memory for non/occupied slots

Currently, a hotplug bridge will be given hpmemsize additional memory if
available, in order to satisfy any future hotplug allocation
requirements.

These calculations don't consider the current memory size of the hotplug
bridge/slot, so hotplug bridges/slots which have downstream devices will
get their current allocation in addition to the hpmemsize value.

This makes for likely undesirable results with a mix of unoccupied and
occupied slots (ex, with hpmemsize=2M):

10000:02:03.0 PCI bridge: <- Occupied
	Memory behind bridge: d6200000-d64fffff [size=3M]
10000:02:04.0 PCI bridge: <- Unoccupied
	Memory behind bridge: d6500000-d66fffff [size=2M]

This change considers the current allocation size when using the
hpmemsize parameter to make the reservations predictable for the mix of
unoccupied and occupied slots:

10000:02:03.0 PCI bridge: <- Occupied
	Memory behind bridge: d6200000-d63fffff [size=2M]
10000:02:04.0 PCI bridge: <- Unoccupied
	Memory behind bridge: d6400000-d65fffff [size=2M]

Signed-off-by: Jon Derrick <jonathan.derrick@...el.com>
---
 drivers/pci/setup-bus.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 79b1824..101c4ee 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -831,7 +831,8 @@ static resource_size_t calculate_iosize(resource_size_t size,
 
 static resource_size_t calculate_memsize(resource_size_t size,
 		resource_size_t min_size,
-		resource_size_t size1,
+		resource_size_t add_size,
+		resource_size_t children_add_size,
 		resource_size_t old_size,
 		resource_size_t align)
 {
@@ -841,7 +842,10 @@ static resource_size_t calculate_memsize(resource_size_t size,
 		old_size = 0;
 	if (size < old_size)
 		size = old_size;
-	size = ALIGN(size + size1, align);
+	size += children_add_size;
+	if (size && add_size >= ALIGN(size, align))
+		add_size -= ALIGN(size, align);
+	size = ALIGN(size + add_size, align);
 	return size;
 }
 
@@ -1079,12 +1083,10 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
 
 	min_align = calculate_mem_align(aligns, max_order);
 	min_align = max(min_align, window_alignment(bus, b_res->flags));
-	size0 = calculate_memsize(size, min_size, 0, resource_size(b_res), min_align);
+	size0 = calculate_memsize(size, min_size, 0, 0, resource_size(b_res), min_align);
 	add_align = max(min_align, add_align);
-	if (children_add_size > add_size)
-		add_size = children_add_size;
-	size1 = (!realloc_head || (realloc_head && !add_size)) ? size0 :
-		calculate_memsize(size, min_size, add_size,
+	size1 = (!realloc_head || (realloc_head && !add_size && !children_add_size)) ? size0 :
+		calculate_memsize(size, min_size, add_size, children_add_size,
 				resource_size(b_res), add_align);
 	if (!size0 && !size1) {
 		if (b_res->start || b_res->end)
-- 
1.8.3.1