Re: [RFC v2 4/5] mm/migrate: Create move_phys_pages syscall
From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Date: 2023-10-02 14:07:56
Also in:
linux-arch, linux-cxl, lkml
On Tue, 19 Sep 2023 19:09:07 -0400 Gregory Price [off-list ref] wrote:
Similar to the move_pages system call, instead of taking a pid and list of virtual addresses, this system call takes a list of physical addresses. Because there is no task to validate the memory policy against, each page needs to be interrogated to determine whether the migration is valid, and all tasks that map it need to be interrogated. This is accomplished in via a rmap_walk on the folio containing the page, and an interrogation of all tasks that map the page (by way of each task's vma). Each page must be interrogated individually, which should be considered when using this to migrate shared regions. The remaining logic is the same as the move_pages syscall. Some minor changes to do_pages_move are made (to check whether an mm_struct is passed) in order to re-use the existing migration code. Signed-off-by: Gregory Price <redacted>
Hi Gregory A few comments inline. Thanks, Jonathan
quoted hunk ↗ jump to hunk
diff --git a/mm/migrate.c b/mm/migrate.c index 1123d841a7f1..2d06557c0b80 100644 --- a/mm/migrate.c +++ b/mm/migrate.c@@ -2165,9 +2165,118 @@ static int move_pages_and_store_status(int node, return store_status(status, start, node, i - start); } +struct rmap_page_ctxt { + bool found; + bool migratable; + bool node_allowed; + int node; +}; + +/* + * Walks each vma mapping a given page and determines if those + * vma's are both migratable, and that the target node is within + * the allowed cpuset of the owning task. + */ +static bool phys_page_migratable(struct folio *folio, + struct vm_area_struct *vma, + unsigned long address, + void *arg) +{ + struct rmap_page_ctxt *ctxt = (struct rmap_page_ctxt *)arg;
arg is a void * so no need for explicit cast.
+ struct task_struct *owner = vma->vm_mm->owner; + /* On non-memcg systems, the allowed set is the possible set */ +#ifdef CONFIG_MEMCG + nodemask_t task_nodes = cpuset_mems_allowed(owner); +#else + nodemask_t task_nodes = node_possible_map; +#endif + + ctxt->found |= true;
Given you or it with true, you might as well just set it.. ctxt->found = true; ends up the same.
+ ctxt->migratable &= vma_migratable(vma); + ctxt->node_allowed &= node_isset(ctxt->node, task_nodes); + + return ctxt->migratable && ctxt->node_allowed; +} +
+/*
+ * Validates the physical address is online and migratable. Walks the folio
+ * containing the page to validate the vma is migratable and the cpuset node
+ * restrictions. Then calls add_page_for_migration to isolate it from the
+ * LRU and place it into the given pagelist.
+ * Returns:
+ * errno - if the page is not online, migratable, or can't be isolated
+ * 0 - when it doesn't have to be migrated because it is already on the
+ * target node
+ * 1 - when it has been queued
+ */
+static int add_phys_page_for_migration(const void __user *p, int node,
+ struct list_head *pagelist,
+ bool migrate_all)
+{
+ unsigned long pfn;
+ struct page *page;
+ struct folio *folio;
+ int err;
+ struct rmap_page_ctxt rmctxt = {
+ .found = false,
+ .migratable = true,
+ .node_allowed = true,
+ .node = node
+ };
+ struct rmap_walk_control rwc = {
+ .rmap_one = phys_page_migratable,
+ .arg = &rmctxt
+ };
+
+ pfn = ((unsigned long)p) >> PAGE_SHIFT;
+ page = pfn_to_online_page(pfn);
+ if (!page || PageTail(page))
+ return -ENOENT;
+
+ folio = phys_migrate_get_folio(page);
+ if (folio)
+ rmap_walk(folio, &rwc);Why not just tidy up the !folio case more directly as if it's not we only get to the first condition as rmctxt.found == false anyway, so this is the same as. if (!folio) return -ENOENT. rmap_walk(foil, &rwc);
+ + if (!rmctxt.found) + err = -ENOENT; + else if (!rmctxt.migratable) + err = -EFAULT; + else if (!rmctxt.node_allowed) + err = -EACCES; + else + err = add_page_for_migration(page, node, pagelist, migrate_all); + + if (folio)
With above changes this condition can go.
quoted hunk ↗ jump to hunk
+ folio_put(folio); + + return err; +} + /* * Migrate an array of page address onto an array of nodes and fill * the corresponding array of status. + * + * When the mm argument is not NULL, task_nodes is expected to be the + * cpuset nodemask for the task which owns the mm_struct, and the + * values located in (*pages) are expected to be virtual addresses. + * + * When the mm argument is NULL, the values located at (*pages) are + * expected to be physical addresses, and task_nodes is expected to + * be empty. */ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes, unsigned long nr_pages,@@ -2181,6 +2290,10 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes, int start, i; int err = 0, err1; + /* This should never occur in regular operation */ + if (!mm && nodes_weight(task_nodes) > 0)
You document below that task_nodes isn't used if !mm but it is used to indicate this condition...
quoted hunk ↗ jump to hunk
+ return -EINVAL; + lru_cache_disable(); for (i = start = 0; i < nr_pages; i++) {@@ -2209,7 +2322,14 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes, goto out_flush; err = -EACCES; - if (!node_isset(node, task_nodes)) + /* + * if mm is NULL, then the pages are addressed via physical + * address and the task_nodes structure is empty. Validation + * of migratability is deferred to add_phys_page_for_migration + * where vma's that map the address will have their node_mask + * checked to ensure the requested node bit is set. + */ + if (mm && !node_isset(node, task_nodes)) goto out_flush;
quoted hunk ↗ jump to hunk
@@ -2317,6 +2444,37 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, mmap_read_unlock(mm); } +/* + * Determine the nodes pages pointed to by the physical addresses in the + * pages array, and store those node values in the status array + */ +static void do_phys_pages_stat_array(unsigned long nr_pages, + const void __user **pages, int *status) +{ + unsigned long i; + + for (i = 0; i < nr_pages; i++) { + unsigned long pfn = (unsigned long)(*pages) >> PAGE_SHIFT; + struct page *page = pfn_to_online_page(pfn); + int err = -ENOENT; + + if (!page) + goto set_status; + + get_page(page); + + if (!is_zone_device_page(page)) + err = page_to_nid(page); + + put_page(page); +set_status: + *status = err;
Given you update it unconditionally this seems to wipe out earlier potential errors with the nid.
+ + pages++; + status++; + } +}
+/*
+ * Move a list of physically-addressed pages to the list of target nodes
+ */
+static int kernel_move_phys_pages(unsigned long nr_pages,
+ const void __user * __user *pages,
+ const int __user *nodes,
+ int __user *status, int flags)
+{
+ int err;
+ nodemask_t dummy_nodes;
+
+ if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))Spaces around the |
+ return -EINVAL; + + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; + + /* + * When the mm argument to do_pages_move is null, the task_nodes + * argument is ignored, so pass in an empty nodemask as a dummy.
If ignored, why bother clearing it? Looks like you are using it as as signal rather than ignoring it. So not sure this comment is correct.
+ */ + nodes_clear(dummy_nodes); + if (nodes) + err = do_pages_move(NULL, dummy_nodes, nr_pages, pages, + nodes, status, flags); + else + err = do_pages_stat(NULL, nr_pages, pages, status); + + return err;
If nothing to do, just return in the two branches and loose the local variable err.
+}
+
+SYSCALL_DEFINE5(move_phys_pages, unsigned long, nr_pages,
+ const void __user * __user *, pages,
+ const int __user *, nodes,
+ int __user *, status, int, flags)
+{
+ return kernel_move_phys_pages(nr_pages, pages, nodes, status, flags);
+}
+Looks like 1 blank line enough to me...
+ #ifdef CONFIG_NUMA_BALANCING