| Message ID | 20091009204126.GD19114@austin.ibm.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
On Fri, 2009-10-09 at 15:41 -0500, Robert Jennings wrote: > The Collaborative Memory Manager (CMM) module allocates individual pages > over time that are not migratable. On a long running system this can > severely impact the ability to find enough pages to support a hotplug > memory remove operation. > > This patch adds a memory isolation notifier and a memory hotplug notifier. > The memory isolation notifier will return the number of pages found > in the range specified. This is used to determine if all of the used > pages in a pageblock are owned by the balloon (or other entities in > the notifier chain). The hotplug notifier will free pages in the range > which is to be removed. The priority of this hotplug notifier is low > so that it will be called near last, this helps avoids removing loaned > pages in operations that fail due to other handlers. > > CMM activity will be halted when hotplug remove operations are active > and resume activity after a delay period to allow the hypervisor time > to adjust. > > Signed-off-by: Robert Jennings <rcj@linux.vnet.ibm.com> Do you need me to merge that via the powerpc tree after the relevant generic parts go in ? This is 2.6.33 material ? > +module_param_named(hotplug_delay, hotplug_delay, uint, S_IRUGO | S_IWUSR); > +MODULE_PARM_DESC(delay, "Delay (in seconds) after memory hotplug remove " > + "before activity resumes. " > + "[Default=" __stringify(CMM_HOTPLUG_DELAY) "]"); What is the above ? That sounds scary :-) > module_param_named(oom_kb, oom_kb, uint, S_IRUGO | S_IWUSR); > MODULE_PARM_DESC(oom_kb, "Amount of memory in kb to free on OOM. " > "[Default=" __stringify(CMM_OOM_KB) "]"); > @@ -88,6 +101,8 @@ struct cmm_page_array { > static unsigned long loaned_pages; > static unsigned long loaned_pages_target; > static unsigned long oom_freed_pages; > +static atomic_t hotplug_active = ATOMIC_INIT(0); > +static atomic_t hotplug_occurred = ATOMIC_INIT(0); That sounds like a hand made lock with atomics... rarely a good idea, tends to miss appropriate barriers etc... > static struct cmm_page_array *cmm_page_list; > static DEFINE_SPINLOCK(cmm_lock); > @@ -110,6 +125,9 @@ static long cmm_alloc_pages(long nr) > cmm_dbg("Begin request for %ld pages\n", nr); > > while (nr) { > + if (atomic_read(&hotplug_active)) > + break; > + Ok so I'm not familiar with that whole memory hotplug stuff, so the code might be right, but wouldn't the above be racy anyways in case hotplug just becomes active after this statement ? Shouldn't you use a mutex_trylock instead ? That has clearer semantics and will provide the appropriate memory barriers. > addr = __get_free_page(GFP_NOIO | __GFP_NOWARN | > __GFP_NORETRY | __GFP_NOMEMALLOC); > if (!addr) > @@ -119,8 +137,10 @@ static long cmm_alloc_pages(long nr) > if (!pa || pa->index >= CMM_NR_PAGES) { > /* Need a new page for the page list. */ > spin_unlock(&cmm_lock); > - npa = (struct cmm_page_array *)__get_free_page(GFP_NOIO | __GFP_NOWARN | > - __GFP_NORETRY | __GFP_NOMEMALLOC); > + npa = (struct cmm_page_array *)__get_free_page( > + GFP_NOIO | __GFP_NOWARN | > + __GFP_NORETRY | __GFP_NOMEMALLOC | > + __GFP_MOVABLE); > if (!npa) { > pr_info("%s: Can not allocate new page list\n", __func__); > free_page(addr); > @@ -273,9 +293,23 @@ static int cmm_thread(void *dummy) > while (1) { > timeleft = msleep_interruptible(delay * 1000); > > - if (kthread_should_stop() || timeleft) { > - loaned_pages_target = loaned_pages; > + if (kthread_should_stop() || timeleft) > break; > + > + if (atomic_read(&hotplug_active)) { > + cmm_dbg("Hotplug operation in progress, activity " > + "suspended\n"); > + continue; > + } > + > + if (atomic_dec_if_positive(&hotplug_occurred) >= 0) { > + cmm_dbg("Hotplug operation has occurred, loaning " > + "activity suspended for %d seconds.\n", > + hotplug_delay); > + timeleft = msleep_interruptible(hotplug_delay * 1000); > + if (kthread_should_stop() || timeleft) > + break; > + continue; > } I have less problems with hotplug_occured but if you use a mutex_trylock, overall, you can turn the above into a normal int instead of an atomic. ../.. > +static int cmm_memory_cb(struct notifier_block *self, > + unsigned long action, void *arg) > +{ > + int ret = 0; > + > + switch (action) { > + case MEM_GOING_OFFLINE: > + atomic_set(&hotplug_active, 1); So that would become a mutex_lock(). Added advantage is that it would wait for a current CMM operation to complete. Cheers, Ben.
* Benjamin Herrenschmidt (benh@kernel.crashing.org) wrote: > On Fri, 2009-10-09 at 15:41 -0500, Robert Jennings wrote: > > The Collaborative Memory Manager (CMM) module allocates individual pages > > over time that are not migratable. On a long running system this can > > severely impact the ability to find enough pages to support a hotplug > > memory remove operation. > > > > This patch adds a memory isolation notifier and a memory hotplug notifier. > > The memory isolation notifier will return the number of pages found > > in the range specified. This is used to determine if all of the used > > pages in a pageblock are owned by the balloon (or other entities in > > the notifier chain). The hotplug notifier will free pages in the range > > which is to be removed. The priority of this hotplug notifier is low > > so that it will be called near last, this helps avoids removing loaned > > pages in operations that fail due to other handlers. > > > > CMM activity will be halted when hotplug remove operations are active > > and resume activity after a delay period to allow the hypervisor time > > to adjust. > > > > Signed-off-by: Robert Jennings <rcj@linux.vnet.ibm.com> > > Do you need me to merge that via the powerpc tree after the relevant > generic parts go in ? This is 2.6.33 material ? I didn't know how this part works honestly, this is the first time I've pushed patches with dependencies like this. Andrew Morton had pulled an earlier version of this and the mm hotplug related changes for 2.6.32. > > +module_param_named(hotplug_delay, hotplug_delay, uint, S_IRUGO | S_IWUSR); > > +MODULE_PARM_DESC(delay, "Delay (in seconds) after memory hotplug remove " > > + "before activity resumes. " > > + "[Default=" __stringify(CMM_HOTPLUG_DELAY) "]"); > > What is the above ? That sounds scary :-) I'm changing this to read "Delay (in seconds) after memory hotplug remove before loaning resumes." in order to clear this us. This is a period where loaning from the balloon is paused after the hotplug completes. This gives the userspace tools time to mark the sections as isolated and unusable with the hypervisor and the hypervisor to take this into account regarding the loaning levels it requests of the OS. > > module_param_named(oom_kb, oom_kb, uint, S_IRUGO | S_IWUSR); > > MODULE_PARM_DESC(oom_kb, "Amount of memory in kb to free on OOM. " > > "[Default=" __stringify(CMM_OOM_KB) "]"); > > @@ -88,6 +101,8 @@ struct cmm_page_array { > > static unsigned long loaned_pages; > > static unsigned long loaned_pages_target; > > static unsigned long oom_freed_pages; > > +static atomic_t hotplug_active = ATOMIC_INIT(0); > > +static atomic_t hotplug_occurred = ATOMIC_INIT(0); > > That sounds like a hand made lock with atomics... rarely a good idea, > tends to miss appropriate barriers etc... > I have changes this so that we have a mutex held during the memory hotplug remove. The hotplug_occurred flag is now and integer protected by the mutex; it is used to provide the delay after the hotplug remove completes. > > static struct cmm_page_array *cmm_page_list; > > static DEFINE_SPINLOCK(cmm_lock); > > @@ -110,6 +125,9 @@ static long cmm_alloc_pages(long nr) > > cmm_dbg("Begin request for %ld pages\n", nr); > > > > while (nr) { > > + if (atomic_read(&hotplug_active)) > > + break; > > + > > Ok so I'm not familiar with that whole memory hotplug stuff, so the code > might be right, but wouldn't the above be racy anyways in case hotplug > just becomes active after this statement ? > > Shouldn't you use a mutex_trylock instead ? That has clearer semantics > and will provide the appropriate memory barriers. I have changed this to use a mutex in the same location. This allows the allocation of pages to terminate early during a hotplug remove operation. If hotplug becomes active after this check in cmm_alloc_pages() one page will be allocated to the balloon, but this page will not belong to the memory range going offline because the pageblock will have already been isolated. After allocating the page we might need to wait on the lock to add the page to the list if hotplug is removing pages from the balloon. After one page is added, cmm_alloc_pages() will exit early when it checks to see if hotplug is active or if it has occurred. I wanted to keep the section locked by cmm_lock small, so that we can safely respond to the hotplug notifier as quickly as possible while minimizing memory pressure. There are no checks in cmm_free_pages() to have it abort early during hotplug memory remove with the rationale that it's good for hotplug to allow the balloon to shrink even if it means holding the cmm_lock a bit longer. > > addr = __get_free_page(GFP_NOIO | __GFP_NOWARN | > > __GFP_NORETRY | __GFP_NOMEMALLOC); > > if (!addr) > > @@ -119,8 +137,10 @@ static long cmm_alloc_pages(long nr) > > if (!pa || pa->index >= CMM_NR_PAGES) { > > /* Need a new page for the page list. */ > > spin_unlock(&cmm_lock); > > - npa = (struct cmm_page_array *)__get_free_page(GFP_NOIO | __GFP_NOWARN | > > - __GFP_NORETRY | __GFP_NOMEMALLOC); > > + npa = (struct cmm_page_array *)__get_free_page( > > + GFP_NOIO | __GFP_NOWARN | > > + __GFP_NORETRY | __GFP_NOMEMALLOC | > > + __GFP_MOVABLE); > > if (!npa) { > > pr_info("%s: Can not allocate new page list\n", __func__); > > free_page(addr); > > @@ -273,9 +293,23 @@ static int cmm_thread(void *dummy) > > while (1) { > > timeleft = msleep_interruptible(delay * 1000); > > > > - if (kthread_should_stop() || timeleft) { > > - loaned_pages_target = loaned_pages; > > + if (kthread_should_stop() || timeleft) > > break; > > + > > + if (atomic_read(&hotplug_active)) { > > + cmm_dbg("Hotplug operation in progress, activity " > > + "suspended\n"); > > + continue; > > + } > > + > > + if (atomic_dec_if_positive(&hotplug_occurred) >= 0) { > > + cmm_dbg("Hotplug operation has occurred, loaning " > > + "activity suspended for %d seconds.\n", > > + hotplug_delay); > > + timeleft = msleep_interruptible(hotplug_delay * 1000); > > + if (kthread_should_stop() || timeleft) > > + break; > > + continue; > > } > > I have less problems with hotplug_occured but if you use a > mutex_trylock, overall, you can turn the above into a normal int instead > of an atomic. Changed to a mutex to indicate that a hotplug operation is active and an int protected by the mutex to indicate that a hotplug operation has occurred. > ../.. > > > +static int cmm_memory_cb(struct notifier_block *self, > > + unsigned long action, void *arg) > > +{ > > + int ret = 0; > > + > > + switch (action) { > > + case MEM_GOING_OFFLINE: > > + atomic_set(&hotplug_active, 1); > > So that would become a mutex_lock(). Added advantage is that > it would wait for a current CMM operation to complete. I've added the mutex but the scope will not prevent hotplug from starting before the current CMM operation has completed. This allows us to abort the allocation. The important globals for managing the list of pages are still covered by the cmm_lock spinlock. I've tested the patch and I'll send it out shortly.
Index: b/arch/powerpc/platforms/pseries/cmm.c =================================================================== --- a/arch/powerpc/platforms/pseries/cmm.c +++ b/arch/powerpc/platforms/pseries/cmm.c @@ -38,19 +38,28 @@ #include <asm/mmu.h> #include <asm/pgalloc.h> #include <asm/uaccess.h> +#include <linux/memory.h> #include "plpar_wrappers.h" #define CMM_DRIVER_VERSION "1.0.0" #define CMM_DEFAULT_DELAY 1 +#define CMM_HOTPLUG_DELAY 5 #define CMM_DEBUG 0 #define CMM_DISABLE 0 #define CMM_OOM_KB 1024 #define CMM_MIN_MEM_MB 256 #define KB2PAGES(_p) ((_p)>>(PAGE_SHIFT-10)) #define PAGES2KB(_p) ((_p)<<(PAGE_SHIFT-10)) +/* + * The priority level tries to ensure that this notifier is called as + * late as possible to reduce thrashing in the shared memory pool. + */ +#define CMM_MEM_HOTPLUG_PRI 1 +#define CMM_MEM_ISOLATE_PRI 15 static unsigned int delay = CMM_DEFAULT_DELAY; +static unsigned int hotplug_delay = CMM_HOTPLUG_DELAY; static unsigned int oom_kb = CMM_OOM_KB; static unsigned int cmm_debug = CMM_DEBUG; static unsigned int cmm_disabled = CMM_DISABLE; @@ -65,6 +74,10 @@ MODULE_VERSION(CMM_DRIVER_VERSION); module_param_named(delay, delay, uint, S_IRUGO | S_IWUSR); MODULE_PARM_DESC(delay, "Delay (in seconds) between polls to query hypervisor paging requests. " "[Default=" __stringify(CMM_DEFAULT_DELAY) "]"); +module_param_named(hotplug_delay, hotplug_delay, uint, S_IRUGO | S_IWUSR); +MODULE_PARM_DESC(delay, "Delay (in seconds) after memory hotplug remove " + "before activity resumes. " + "[Default=" __stringify(CMM_HOTPLUG_DELAY) "]"); module_param_named(oom_kb, oom_kb, uint, S_IRUGO | S_IWUSR); MODULE_PARM_DESC(oom_kb, "Amount of memory in kb to free on OOM. " "[Default=" __stringify(CMM_OOM_KB) "]"); @@ -88,6 +101,8 @@ struct cmm_page_array { static unsigned long loaned_pages; static unsigned long loaned_pages_target; static unsigned long oom_freed_pages; +static atomic_t hotplug_active = ATOMIC_INIT(0); +static atomic_t hotplug_occurred = ATOMIC_INIT(0); static struct cmm_page_array *cmm_page_list; static DEFINE_SPINLOCK(cmm_lock); @@ -110,6 +125,9 @@ static long cmm_alloc_pages(long nr) cmm_dbg("Begin request for %ld pages\n", nr); while (nr) { + if (atomic_read(&hotplug_active)) + break; + addr = __get_free_page(GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC); if (!addr) @@ -119,8 +137,10 @@ static long cmm_alloc_pages(long nr) if (!pa || pa->index >= CMM_NR_PAGES) { /* Need a new page for the page list. */ spin_unlock(&cmm_lock); - npa = (struct cmm_page_array *)__get_free_page(GFP_NOIO | __GFP_NOWARN | - __GFP_NORETRY | __GFP_NOMEMALLOC); + npa = (struct cmm_page_array *)__get_free_page( + GFP_NOIO | __GFP_NOWARN | + __GFP_NORETRY | __GFP_NOMEMALLOC | + __GFP_MOVABLE); if (!npa) { pr_info("%s: Can not allocate new page list\n", __func__); free_page(addr); @@ -273,9 +293,23 @@ static int cmm_thread(void *dummy) while (1) { timeleft = msleep_interruptible(delay * 1000); - if (kthread_should_stop() || timeleft) { - loaned_pages_target = loaned_pages; + if (kthread_should_stop() || timeleft) break; + + if (atomic_read(&hotplug_active)) { + cmm_dbg("Hotplug operation in progress, activity " + "suspended\n"); + continue; + } + + if (atomic_dec_if_positive(&hotplug_occurred) >= 0) { + cmm_dbg("Hotplug operation has occurred, loaning " + "activity suspended for %d seconds.\n", + hotplug_delay); + timeleft = msleep_interruptible(hotplug_delay * 1000); + if (kthread_should_stop() || timeleft) + break; + continue; } cmm_get_mpp(); @@ -405,6 +439,159 @@ static struct notifier_block cmm_reboot_ }; /** + * cmm_count_pages - Count the number of pages loaned in a particular range. + * + * @arg: memory_isolate_notify structure with address range and count + * + * Return value: + * 0 on success + **/ +static unsigned long cmm_count_pages(void *arg) +{ + struct memory_isolate_notify *marg = arg; + struct cmm_page_array *pa; + unsigned long start = (unsigned long)pfn_to_kaddr(marg->start_pfn); + unsigned long end = start + (marg->nr_pages << PAGE_SHIFT); + unsigned long idx; + + spin_lock(&cmm_lock); + pa = cmm_page_list; + while (pa) { + for (idx = 0; idx < pa->index; idx++) + if (pa->page[idx] >= start && pa->page[idx] < end) + marg->pages_found++; + pa = pa->next; + } + spin_unlock(&cmm_lock); + return 0; +} + +/** + * cmm_memory_isolate_cb - Handle memory isolation notifier calls + * @self: notifier block struct + * @action: action to take + * @arg: struct memory_isolate_notify data for handler + * + * Return value: + * NOTIFY_OK or notifier error based on subfunction return value + **/ +static int cmm_memory_isolate_cb(struct notifier_block *self, + unsigned long action, void *arg) +{ + int ret = 0; + + if (action == MEM_ISOLATE_COUNT) + ret = cmm_count_pages(arg); + + if (ret) + ret = notifier_from_errno(ret); + else + ret = NOTIFY_OK; + + return ret; +} + +static struct notifier_block cmm_mem_isolate_nb = { + .notifier_call = cmm_memory_isolate_cb, + .priority = CMM_MEM_ISOLATE_PRI +}; + +/** + * cmm_mem_going_offline - Unloan pages where memory is to be removed + * @arg: memory_notify structure with page range to be offlined + * + * Return value: + * 0 on success + **/ +static int cmm_mem_going_offline(void *arg) +{ + struct memory_notify *marg = arg; + unsigned long start_page = (unsigned long)pfn_to_kaddr(marg->start_pfn); + unsigned long end_page = start_page + (marg->nr_pages << PAGE_SHIFT); + struct cmm_page_array *pa_curr, *pa_last; + unsigned long idx; + unsigned long freed = 0; + + cmm_dbg("Memory going offline, searching 0x%lx (%ld pages).\n", + start_page, marg->nr_pages); + spin_lock(&cmm_lock); + + pa_last = pa_curr = cmm_page_list; + while (pa_curr) { + for (idx = (pa_curr->index - 1); (idx + 1) > 0; idx--) { + if ((pa_curr->page[idx] < start_page) || + (pa_curr->page[idx] >= end_page)) + continue; + + plpar_page_set_active(__pa(pa_curr->page[idx])); + free_page(pa_curr->page[idx]); + freed++; + loaned_pages--; + totalram_pages++; + pa_curr->page[idx] = pa_last->page[--pa_last->index]; + if (pa_last->index == 0) { + if (pa_curr == pa_last) + pa_curr = pa_last->next; + pa_last = pa_last->next; + free_page((unsigned long)cmm_page_list); + cmm_page_list = pa_last; + continue; + } + } + pa_curr = pa_curr->next; + } + atomic_set(&hotplug_occurred, 1); + spin_unlock(&cmm_lock); + cmm_dbg("Released %ld pages in the search range.\n", freed); + + return 0; +} + +/** + * cmm_memory_cb - Handle memory hotplug notifier calls + * @self: notifier block struct + * @action: action to take + * @arg: struct memory_notify data for handler + * + * Return value: + * NOTIFY_OK or notifier error based on subfunction return value + * + **/ +static int cmm_memory_cb(struct notifier_block *self, + unsigned long action, void *arg) +{ + int ret = 0; + + switch (action) { + case MEM_GOING_OFFLINE: + atomic_set(&hotplug_active, 1); + ret = cmm_mem_going_offline(arg); + break; + case MEM_OFFLINE: + case MEM_CANCEL_OFFLINE: + atomic_set(&hotplug_active, 0); + cmm_dbg("Memory offline operation complete.\n"); + break; + case MEM_GOING_ONLINE: + case MEM_ONLINE: + case MEM_CANCEL_ONLINE: + break; + } + + if (ret) + ret = notifier_from_errno(ret); + else + ret = NOTIFY_OK; + + return ret; +} + +static struct notifier_block cmm_mem_nb = { + .notifier_call = cmm_memory_cb, + .priority = CMM_MEM_HOTPLUG_PRI +}; + +/** * cmm_init - Module initialization * * Return value: @@ -426,18 +613,24 @@ static int cmm_init(void) if ((rc = cmm_sysfs_register(&cmm_sysdev))) goto out_reboot_notifier; + if (register_memory_notifier(&cmm_mem_nb) || + register_memory_isolate_notifier(&cmm_mem_isolate_nb)) + goto out_unregister_notifier; + if (cmm_disabled) return rc; cmm_thread_ptr = kthread_run(cmm_thread, NULL, "cmmthread"); if (IS_ERR(cmm_thread_ptr)) { rc = PTR_ERR(cmm_thread_ptr); - goto out_unregister_sysfs; + goto out_unregister_notifier; } return rc; -out_unregister_sysfs: +out_unregister_notifier: + unregister_memory_notifier(&cmm_mem_nb); + unregister_memory_isolate_notifier(&cmm_mem_isolate_nb); cmm_unregister_sysfs(&cmm_sysdev); out_reboot_notifier: unregister_reboot_notifier(&cmm_reboot_nb); @@ -458,6 +651,8 @@ static void cmm_exit(void) kthread_stop(cmm_thread_ptr); unregister_oom_notifier(&cmm_oom_nb); unregister_reboot_notifier(&cmm_reboot_nb); + unregister_memory_notifier(&cmm_mem_nb); + unregister_memory_isolate_notifier(&cmm_mem_isolate_nb); cmm_free_pages(loaned_pages); cmm_unregister_sysfs(&cmm_sysdev); }
The Collaborative Memory Manager (CMM) module allocates individual pages over time that are not migratable. On a long running system this can severely impact the ability to find enough pages to support a hotplug memory remove operation. This patch adds a memory isolation notifier and a memory hotplug notifier. The memory isolation notifier will return the number of pages found in the range specified. This is used to determine if all of the used pages in a pageblock are owned by the balloon (or other entities in the notifier chain). The hotplug notifier will free pages in the range which is to be removed. The priority of this hotplug notifier is low so that it will be called near last, this helps avoids removing loaned pages in operations that fail due to other handlers. CMM activity will be halted when hotplug remove operations are active and resume activity after a delay period to allow the hypervisor time to adjust. Signed-off-by: Robert Jennings <rcj@linux.vnet.ibm.com> --- I'm not entirely sure of the ettiquette, but there are no changes to this patch. I'm resending to keep it with the changes to the parent patch. arch/powerpc/platforms/pseries/cmm.c | 207 ++++++++++++++++++++++++++++++++++- 1 file changed, 201 insertions(+), 6 deletions(-)