This patch shows one approach to associating a specific mem cgroup to
an mshare file and was inspired by code in mem_cgroup_sk_alloc().
Essentially when a process creates an mshare region, a reference is
taken on the mem cgroup that the process belongs to and a pointer to
the memcg is saved. At fault time set_active_memcg() is used to
temporarily enable charging of __GFP_ACCOUNT allocations to the saved
memcg. This does consolidate pagetable charges to a single memcg, but
there are issues to address such as how to handle the case where the
memcg is deleted but becomes a hidden, zombie memcg because the mshare
file has a reference to it.
Signed-off-by: Anthony Yznaga <anthony.yznaga@xxxxxxxxxx>
---
arch/x86/mm/fault.c | 11 +++++++++++
include/linux/mm.h | 5 +++++
mm/mshare.c | 33 +++++++++++++++++++++++++++++++++
3 files changed, 49 insertions(+)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 4b55ade61a01..1b50417f68ad 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -21,6 +21,7 @@
#include <linux/mm_types.h>
#include <linux/mm.h> /* find_and_lock_vma() */
#include <linux/vmalloc.h>
+#include <linux/memcontrol.h>
#include <asm/cpufeature.h> /* boot_cpu_has, ... */
#include <asm/traps.h> /* dotraplinkage, ... */
@@ -1219,6 +1220,8 @@ void do_user_addr_fault(struct pt_regs *regs,
unsigned int flags = FAULT_FLAG_DEFAULT;
bool is_shared_vma;
unsigned long addr;
+ struct mem_cgroup *mshare_memcg;
+ struct mem_cgroup *memcg;
tsk = current;
mm = tsk->mm;
@@ -1375,6 +1378,8 @@ void do_user_addr_fault(struct pt_regs *regs,
}
if (unlikely(vma_is_mshare(vma))) {
+ mshare_memcg = get_mshare_memcg(vma);
+
fault = find_shared_vma(&vma, &addr);
if (fault) {
@@ -1402,6 +1407,9 @@ void do_user_addr_fault(struct pt_regs *regs,
return;
}
+ if (is_shared_vma && mshare_memcg)
+ memcg = set_active_memcg(mshare_memcg);
+
/*
* If for any reason at all we couldn't handle the fault,
* make sure we exit gracefully rather than endlessly redo
@@ -1417,6 +1425,9 @@ void do_user_addr_fault(struct pt_regs *regs,
*/
fault = handle_mm_fault(vma, addr, flags, regs);
+ if (is_shared_vma && mshare_memcg)
+ set_active_memcg(memcg);
+
if (unlikely(is_shared_vma) && ((fault & VM_FAULT_COMPLETED) ||
(fault & VM_FAULT_RETRY) || fault_signal_pending(fault, regs)))
mmap_read_unlock(mm);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 80429d1a6ae4..eaa304d22a9d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1110,12 +1110,17 @@ static inline bool vma_is_anon_shmem(struct vm_area_struct *vma) { return false;
int vma_is_stack_for_current(struct vm_area_struct *vma);
#ifdef CONFIG_MSHARE
+struct mem_cgroup *get_mshare_memcg(struct vm_area_struct *vma);
vm_fault_t find_shared_vma(struct vm_area_struct **vma, unsigned long *addrp);
static inline bool vma_is_mshare(const struct vm_area_struct *vma)
{
return vma->vm_flags & VM_MSHARE;
}
#else
+static inline struct mem_cgroup *get_mshare_memcg(struct vm_area_struct *vma)
+{
+ return NULL;
+}
static inline vm_fault_t find_shared_vma(struct vm_area_struct **vma, unsigned long *addrp)
{
WARN_ON_ONCE(1);
diff --git a/mm/mshare.c b/mm/mshare.c
index 5cc416cfd78c..a56e56c90aaa 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -16,6 +16,7 @@
#include <linux/fs.h>
#include <linux/fs_context.h>
+#include <linux/memcontrol.h>
#include <linux/mman.h>
#include <linux/mmu_notifier.h>
#include <linux/spinlock_types.h>
@@ -30,8 +31,22 @@ struct mshare_data {
spinlock_t m_lock;
struct mshare_info minfo;
struct mmu_notifier mn;
+#ifdef CONFIG_MEMCG
+ struct mem_cgroup *memcg;
+#endif
};
+struct mem_cgroup *get_mshare_memcg(struct vm_area_struct *vma)
+{
+ struct mshare_data *m_data = vma->vm_private_data;
+
+#ifdef CONFIG_MEMCG
+ return m_data->memcg;
+#else
+ return NULL;
+#endif
+}
+
static void mshare_invalidate_tlbs(struct mmu_notifier *mn, struct mm_struct *mm,
unsigned long start, unsigned long end)
{
@@ -358,6 +373,9 @@ msharefs_fill_mm(struct inode *inode)
struct mm_struct *mm;
struct mshare_data *m_data = NULL;
int ret = 0;
+#ifdef CONFIG_MEMCG
+ struct mem_cgroup *memcg;
+#endif
mm = mm_alloc();
if (!mm) {
@@ -383,6 +401,17 @@ msharefs_fill_mm(struct inode *inode)
#ifdef CONFIG_MEMCG
mm->owner = NULL;
+
+ rcu_read_lock();
+ memcg = mem_cgroup_from_task(current);
+ if (mem_cgroup_is_root(memcg))
+ goto out;
+ if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
+ goto out;
+ if (css_tryget(&memcg->css))
+ m_data->memcg = memcg;
+out:
+ rcu_read_unlock();
#endif
return 0;
@@ -396,6 +425,10 @@ msharefs_fill_mm(struct inode *inode)
static void
msharefs_delmm(struct mshare_data *m_data)
{
+#ifdef CONFIG_MEMCG
+ if (m_data->memcg)
+ css_put(&m_data->memcg->css);
+#endif
mmput(m_data->mm);
kfree(m_data);
}
--
2.43.5
