memcg: mem_cgroup_charge never NULL
My memcgroup patch to fix hang with shmem/tmpfs added NULL page handling to
mem_cgroup_charge_common. It seemed convenient at the time, but hard to
justify now: there's a perfectly appropriate swappage to charge and uncharge
instead, this is not on any hot path through shmem_getpage, and no performance
hit was observed from the slight extra overhead.
So revert that NULL page handling from mem_cgroup_charge_common; and make it
clearer by bringing page_cgroup_assign_new_page_cgroup into its body - that
was a helper I found more of a hindrance to understanding.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: David Rientjes <rientjes@google.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hirokazu Takahashi <taka@valinux.co.jp>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9e170d3..83ba13a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -301,25 +301,6 @@
}
/*
- * Tie new page_cgroup to struct page under lock_page_cgroup()
- * This can fail if the page has been tied to a page_cgroup.
- * If success, returns 0.
- */
-static int page_cgroup_assign_new_page_cgroup(struct page *page,
- struct page_cgroup *pc)
-{
- int ret = 0;
-
- lock_page_cgroup(page);
- if (!page_get_page_cgroup(page))
- page_assign_page_cgroup(page, pc);
- else /* A page is tied to other pc. */
- ret = 1;
- unlock_page_cgroup(page);
- return ret;
-}
-
-/*
* Clear page->page_cgroup member under lock_page_cgroup().
* If given "pc" value is different from one page->page_cgroup,
* page->cgroup is not cleared.
@@ -585,26 +566,24 @@
* with it
*/
retry:
- if (page) {
- lock_page_cgroup(page);
- pc = page_get_page_cgroup(page);
- /*
- * The page_cgroup exists and
- * the page has already been accounted.
- */
- if (pc) {
- if (unlikely(!atomic_inc_not_zero(&pc->ref_cnt))) {
- /* this page is under being uncharged ? */
- unlock_page_cgroup(page);
- cpu_relax();
- goto retry;
- } else {
- unlock_page_cgroup(page);
- goto done;
- }
+ lock_page_cgroup(page);
+ pc = page_get_page_cgroup(page);
+ /*
+ * The page_cgroup exists and
+ * the page has already been accounted.
+ */
+ if (pc) {
+ if (unlikely(!atomic_inc_not_zero(&pc->ref_cnt))) {
+ /* this page is under being uncharged ? */
+ unlock_page_cgroup(page);
+ cpu_relax();
+ goto retry;
+ } else {
+ unlock_page_cgroup(page);
+ goto done;
}
- unlock_page_cgroup(page);
}
+ unlock_page_cgroup(page);
pc = kzalloc(sizeof(struct page_cgroup), gfp_mask);
if (pc == NULL)
@@ -663,7 +642,9 @@
if (ctype == MEM_CGROUP_CHARGE_TYPE_CACHE)
pc->flags |= PAGE_CGROUP_FLAG_CACHE;
- if (!page || page_cgroup_assign_new_page_cgroup(page, pc)) {
+ lock_page_cgroup(page);
+ if (page_get_page_cgroup(page)) {
+ unlock_page_cgroup(page);
/*
* Another charge has been added to this page already.
* We take lock_page_cgroup(page) again and read
@@ -672,10 +653,10 @@
res_counter_uncharge(&mem->res, PAGE_SIZE);
css_put(&mem->css);
kfree(pc);
- if (!page)
- goto done;
goto retry;
}
+ page_assign_page_cgroup(page, pc);
+ unlock_page_cgroup(page);
mz = page_cgroup_zoneinfo(pc);
spin_lock_irqsave(&mz->lru_lock, flags);
diff --git a/mm/shmem.c b/mm/shmem.c
index 90b576c..3372bc5 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1370,14 +1370,17 @@
shmem_swp_unmap(entry);
spin_unlock(&info->lock);
unlock_page(swappage);
- page_cache_release(swappage);
if (error == -ENOMEM) {
/* allow reclaim from this memory cgroup */
- error = mem_cgroup_cache_charge(NULL,
+ error = mem_cgroup_cache_charge(swappage,
current->mm, gfp & ~__GFP_HIGHMEM);
- if (error)
+ if (error) {
+ page_cache_release(swappage);
goto failed;
+ }
+ mem_cgroup_uncharge_page(swappage);
}
+ page_cache_release(swappage);
goto repeat;
}
} else if (sgp == SGP_READ && !filepage) {