The patch titled
Subject: drivers/base/memory.c: indicate all memory blocks as removable
has been removed from the -mm tree. Its filename was
drivers-base-memoryc-indicate-all-memory-blocks-as-removable.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: David Hildenbrand <david(a)redhat.com>
Subject: drivers/base/memory.c: indicate all memory blocks as removable
We see multiple issues with the implementation/interface to compute
whether a memory block can be offlined (exposed via
/sys/devices/system/memory/memoryX/removable) and would like to simplify
it (remove the implementation).
1. It runs basically lockless. While this might be good for performance,
we see possible races with memory offlining that will require at least
some sort of locking to fix.
2. Nowadays, more false positives are possible. No arch-specific checks
are performed that validate if memory offlining will not be denied
right away (and such check will require locking). For example, arm64
won't allow to offline any memory block that was added during boot -
which will imply a very high error rate. Other archs have other
constraints.
3. The interface is inherently racy. E.g., if a memory block is
detected to be removable (and was not a false positive at that time),
there is still no guarantee that offlining will actually succeed. So
any caller already has to deal with false positives.
4. It is unclear which performance benefit this interface actually
provides. The introducing commit 5c755e9fd813 ("memory-hotplug: add
sysfs removable attribute for hotplug memory remove") mentioned
"A user-level agent must be able to identify which sections of
memory are likely to be removable before attempting the
potentially expensive operation."
However, no actual performance comparison was included.
Known users:
- lsmem: Will group memory blocks based on the "removable" property. [1]
- chmem: Indirect user. It has a RANGE mode where one can specify
removable ranges identified via lsmem to be offlined. However, it
also has a "SIZE" mode, which allows a sysadmin to skip the manual
"identify removable blocks" step. [2]
- powerpc-utils: Uses the "removable" attribute to skip some memory
blocks right away when trying to find some to
offline+remove. However, with ballooning enabled, it
already skips this information completely (because it
once resulted in many false negatives). Therefore, the
implementation can deal with false positives properly
already. [3]
According to Nathan Fontenot, DLPAR on powerpc is nowadays no longer
driven from userspace via the drmgr command (powerpc-utils). Nowadays
it's managed in the kernel - including onlining/offlining of memory
blocks - triggered by drmgr writing to /sys/kernel/dlpar. So the
affected legacy userspace handling is only active on old kernels. Only ve=
ry
old versions of drmgr on a new kernel (unlikely) might execute slower -
totally acceptable.
With CONFIG_MEMORY_HOTREMOVE, always indicating "removable" should not
break any user space tool. We implement a very bad heuristic now. Withou=
t
CONFIG_MEMORY_HOTREMOVE we cannot offline anything, so report
"not removable" as before.
Original discussion can be found in [4] ("[PATCH RFC v1] mm:
is_mem_section_removable() overhaul").
Other users of is_mem_section_removable() will be removed next, so that
we can remove is_mem_section_removable() completely.
[1] http://man7.org/linux/man-pages/man1/lsmem.1.html
[2] http://man7.org/linux/man-pages/man8/chmem.8.html
[3] https://github.com/ibm-power-utilities/powerpc-utils
[4] https://lkml.kernel.org/r/20200117105759.27905-1-david@redhat.com
Also, this patch probably fixes a crash reported by Steve.
http://lkml.kernel.org/r/CAPcyv4jpdaNvJ67SkjyUJLBnBnXXQv686BiVW042g03FUmWLX…
Link: http://lkml.kernel.org/r/20200128093542.6908-1-david@redhat.com
Signed-off-by: David Hildenbrand <david(a)redhat.com>
Suggested-by: Michal Hocko <mhocko(a)kernel.org>
Acked-by: Michal Hocko <mhocko(a)suse.com>
Reviewed-by: Nathan Fontenot <ndfont(a)gmail.com>
Reported-by: "Scargall, Steve" <steve.scargall(a)intel.com>
Cc: Dan Williams <dan.j.williams(a)intel.com>
Cc: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael(a)kernel.org>
Cc: Badari Pulavarty <pbadari(a)us.ibm.com>
Cc: Robert Jennings <rcj(a)linux.vnet.ibm.com>
Cc: Heiko Carstens <heiko.carstens(a)de.ibm.com>
Cc: Karel Zak <kzak(a)redhat.com>
Cc: <stable(a)vger.kernel.org>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
---
drivers/base/memory.c | 23 +++--------------------
1 file changed, 3 insertions(+), 20 deletions(-)
--- a/drivers/base/memory.c~drivers-base-memoryc-indicate-all-memory-blocks-as-removable
+++ a/drivers/base/memory.c
@@ -97,30 +97,13 @@ static ssize_t phys_index_show(struct de
}
/*
- * Show whether the memory block is likely to be offlineable (or is already
- * offline). Once offline, the memory block could be removed. The return
- * value does, however, not indicate that there is a way to remove the
- * memory block.
+ * Legacy interface that we cannot remove. Always indicate "removable"
+ * with CONFIG_MEMORY_HOTREMOVE - bad heuristic.
*/
static ssize_t removable_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
- struct memory_block *mem = to_memory_block(dev);
- unsigned long pfn;
- int ret = 1, i;
-
- if (mem->state != MEM_ONLINE)
- goto out;
-
- for (i = 0; i < sections_per_block; i++) {
- if (!present_section_nr(mem->start_section_nr + i))
- continue;
- pfn = section_nr_to_pfn(mem->start_section_nr + i);
- ret &= is_mem_section_removable(pfn, PAGES_PER_SECTION);
- }
-
-out:
- return sprintf(buf, "%d\n", ret);
+ return sprintf(buf, "%d\n", (int)IS_ENABLED(CONFIG_MEMORY_HOTREMOVE));
}
/*
_
Patches currently in -mm which might be from david(a)redhat.com are
drivers-base-memoryc-cache-memory-blocks-in-xarray-to-accelerate-lookup-fix.patch
virtio-balloon-switch-back-to-oom-handler-for-virtio_balloon_f_deflate_on_oom.patch
drivers-base-memoryc-drop-section_count.patch
drivers-base-memoryc-drop-pages_correctly_probed.patch
mm-page_extc-drop-pfn_present-check-when-onlining.patch
mm-memory_hotplug-simplify-calculation-of-number-of-pages-in-__remove_pages.patch
mm-memory_hotplug-cleanup-__add_pages.patch
drivers-base-memory-rename-mmop_online_keep-to-mmop_online.patch
drivers-base-memory-map-mmop_offline-to-0.patch
drivers-base-memory-store-mapping-between-mmop_-and-string-in-an-array.patch
powernv-memtrace-always-online-added-memory-blocks.patch
hv_balloon-dont-check-for-memhp_auto_online-manually.patch
mm-memory_hotplug-unexport-memhp_auto_online.patch
mm-memory_hotplug-convert-memhp_auto_online-to-store-an-online_type.patch
mm-memory_hotplug-allow-to-specify-a-default-online_type.patch
The patch titled
Subject: mm/swapfile.c: move inode_lock out of claim_swapfile
has been removed from the -mm tree. Its filename was
mm-swap-move-inode_lock-out-of-claim_swapfile.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Naohiro Aota <naohiro.aota(a)wdc.com>
Subject: mm/swapfile.c: move inode_lock out of claim_swapfile
claim_swapfile() currently keeps the inode locked when it is successful,
or the file is already swapfile (with -EBUSY). And, on the other error
cases, it does not lock the inode.
This inconsistency of the lock state and return value is quite confusing
and actually causing a bad unlock balance as below in the "bad_swap"
section of __do_sys_swapon().
This commit fixes this issue by moving the inode_lock() and IS_SWAPFILE
check out of claim_swapfile(). The inode is unlocked in
"bad_swap_unlock_inode" section, so that the inode is ensured to be
unlocked at "bad_swap". Thus, error handling codes after the locking now
jumps to "bad_swap_unlock_inode" instead of "bad_swap".
=====================================
WARNING: bad unlock balance detected!
5.5.0-rc7+ #176 Not tainted
-------------------------------------
swapon/4294 is trying to release lock (&sb->s_type->i_mutex_key) at:
[<ffffffff8173a6eb>] __do_sys_swapon+0x94b/0x3550
but there are no more locks to release!
other info that might help us debug this:
no locks held by swapon/4294.
stack backtrace:
CPU: 5 PID: 4294 Comm: swapon Not tainted 5.5.0-rc7-BTRFS-ZNS+ #176
Hardware name: ASUS All Series/H87-PRO, BIOS 2102 07/29/2014
Call Trace:
dump_stack+0xa1/0xea
? __do_sys_swapon+0x94b/0x3550
print_unlock_imbalance_bug.cold+0x114/0x123
? __do_sys_swapon+0x94b/0x3550
lock_release+0x562/0xed0
? kvfree+0x31/0x40
? lock_downgrade+0x770/0x770
? kvfree+0x31/0x40
? rcu_read_lock_sched_held+0xa1/0xd0
? rcu_read_lock_bh_held+0xb0/0xb0
up_write+0x2d/0x490
? kfree+0x293/0x2f0
__do_sys_swapon+0x94b/0x3550
? putname+0xb0/0xf0
? kmem_cache_free+0x2e7/0x370
? do_sys_open+0x184/0x3e0
? generic_max_swapfile_size+0x40/0x40
? do_syscall_64+0x27/0x4b0
? entry_SYSCALL_64_after_hwframe+0x49/0xbe
? lockdep_hardirqs_on+0x38c/0x590
__x64_sys_swapon+0x54/0x80
do_syscall_64+0xa4/0x4b0
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f15da0a0dc7
Link: http://lkml.kernel.org/r/20200206090132.154869-1-naohiro.aota@wdc.com
Fixes: 1638045c3677 ("mm: set S_SWAPFILE on blockdev swap devices")
Signed-off-by: Naohiro Aota <naohiro.aota(a)wdc.com>
Reviewed-by: Andrew Morton <akpm(a)linux-foundation.org>
Reviewed-by: Darrick J. Wong <darrick.wong(a)oracle.com>
Tested-by: Qais Youef <qais.yousef(a)arm.com>
Cc: Christoph Hellwig <hch(a)infradead.org>
Cc: <stable(a)vger.kernel.org>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
---
mm/swapfile.c | 41 ++++++++++++++++++++---------------------
1 file changed, 20 insertions(+), 21 deletions(-)
--- a/mm/swapfile.c~mm-swap-move-inode_lock-out-of-claim_swapfile
+++ a/mm/swapfile.c
@@ -2899,10 +2899,6 @@ static int claim_swapfile(struct swap_in
p->bdev = inode->i_sb->s_bdev;
}
- inode_lock(inode);
- if (IS_SWAPFILE(inode))
- return -EBUSY;
-
return 0;
}
@@ -3157,36 +3153,41 @@ SYSCALL_DEFINE2(swapon, const char __use
mapping = swap_file->f_mapping;
inode = mapping->host;
- /* will take i_rwsem; */
error = claim_swapfile(p, inode);
if (unlikely(error))
goto bad_swap;
+ inode_lock(inode);
+ if (IS_SWAPFILE(inode)) {
+ error = -EBUSY;
+ goto bad_swap_unlock_inode;
+ }
+
/*
* Read the swap header.
*/
if (!mapping->a_ops->readpage) {
error = -EINVAL;
- goto bad_swap;
+ goto bad_swap_unlock_inode;
}
page = read_mapping_page(mapping, 0, swap_file);
if (IS_ERR(page)) {
error = PTR_ERR(page);
- goto bad_swap;
+ goto bad_swap_unlock_inode;
}
swap_header = kmap(page);
maxpages = read_swap_header(p, swap_header, inode);
if (unlikely(!maxpages)) {
error = -EINVAL;
- goto bad_swap;
+ goto bad_swap_unlock_inode;
}
/* OK, set up the swap map and apply the bad block list */
swap_map = vzalloc(maxpages);
if (!swap_map) {
error = -ENOMEM;
- goto bad_swap;
+ goto bad_swap_unlock_inode;
}
if (bdi_cap_stable_pages_required(inode_to_bdi(inode)))
@@ -3211,7 +3212,7 @@ SYSCALL_DEFINE2(swapon, const char __use
GFP_KERNEL);
if (!cluster_info) {
error = -ENOMEM;
- goto bad_swap;
+ goto bad_swap_unlock_inode;
}
for (ci = 0; ci < nr_cluster; ci++)
@@ -3220,7 +3221,7 @@ SYSCALL_DEFINE2(swapon, const char __use
p->percpu_cluster = alloc_percpu(struct percpu_cluster);
if (!p->percpu_cluster) {
error = -ENOMEM;
- goto bad_swap;
+ goto bad_swap_unlock_inode;
}
for_each_possible_cpu(cpu) {
struct percpu_cluster *cluster;
@@ -3234,13 +3235,13 @@ SYSCALL_DEFINE2(swapon, const char __use
error = swap_cgroup_swapon(p->type, maxpages);
if (error)
- goto bad_swap;
+ goto bad_swap_unlock_inode;
nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
cluster_info, maxpages, &span);
if (unlikely(nr_extents < 0)) {
error = nr_extents;
- goto bad_swap;
+ goto bad_swap_unlock_inode;
}
/* frontswap enabled? set up bit-per-page map for frontswap */
if (IS_ENABLED(CONFIG_FRONTSWAP))
@@ -3280,7 +3281,7 @@ SYSCALL_DEFINE2(swapon, const char __use
error = init_swap_address_space(p->type, maxpages);
if (error)
- goto bad_swap;
+ goto bad_swap_unlock_inode;
/*
* Flush any pending IO and dirty mappings before we start using this
@@ -3290,7 +3291,7 @@ SYSCALL_DEFINE2(swapon, const char __use
error = inode_drain_writes(inode);
if (error) {
inode->i_flags &= ~S_SWAPFILE;
- goto bad_swap;
+ goto bad_swap_unlock_inode;
}
mutex_lock(&swapon_mutex);
@@ -3315,6 +3316,8 @@ SYSCALL_DEFINE2(swapon, const char __use
error = 0;
goto out;
+bad_swap_unlock_inode:
+ inode_unlock(inode);
bad_swap:
free_percpu(p->percpu_cluster);
p->percpu_cluster = NULL;
@@ -3322,6 +3325,7 @@ bad_swap:
set_blocksize(p->bdev, p->old_block_size);
blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
}
+ inode = NULL;
destroy_swap_extents(p);
swap_cgroup_swapoff(p->type);
spin_lock(&swap_lock);
@@ -3333,13 +3337,8 @@ bad_swap:
kvfree(frontswap_map);
if (inced_nr_rotate_swap)
atomic_dec(&nr_rotate_swap);
- if (swap_file) {
- if (inode) {
- inode_unlock(inode);
- inode = NULL;
- }
+ if (swap_file)
filp_close(swap_file, NULL);
- }
out:
if (page && !IS_ERR(page)) {
kunmap(page);
_
Patches currently in -mm which might be from naohiro.aota(a)wdc.com are