The patch titled
Subject: mm: drop mmap_sem before calling balance_dirty_pages() in write fault
has been added to the -mm tree. Its filename is
mm-drop-mmap_sem-before-calling-balance_dirty_pages-in-write-fault.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-drop-mmap_sem-before-calling-balance_dirty_pages-in-write-fault.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-drop-mmap_sem-before-calling-balance_dirty_pages-in-write-fault.patch
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------------------------------------------------------
From: Johannes Weiner <hannes@xxxxxxxxxxx>
Subject: mm: drop mmap_sem before calling balance_dirty_pages() in write fault
One of our services is observing hanging ps/top/etc under heavy write IO,
and the task states show this is an mmap_sem priority inversion:
A write fault is holding the mmap_sem in read-mode and waiting for
(heavily cgroup-limited) IO in balance_dirty_pages():
[<0>] balance_dirty_pages+0x724/0x905
[<0>] balance_dirty_pages_ratelimited+0x254/0x390
[<0>] fault_dirty_shared_page.isra.96+0x4a/0x90
[<0>] do_wp_page+0x33e/0x400
[<0>] __handle_mm_fault+0x6f0/0xfa0
[<0>] handle_mm_fault+0xe4/0x200
[<0>] __do_page_fault+0x22b/0x4a0
[<0>] page_fault+0x45/0x50
[<0>] 0xffffffffffffffff
Somebody tries to change the address space, contending for the mmap_sem in
write-mode:
[<0>] call_rwsem_down_write_failed_killable+0x13/0x20
[<0>] do_mprotect_pkey+0xa8/0x330
[<0>] SyS_mprotect+0xf/0x20
[<0>] do_syscall_64+0x5b/0x100
[<0>] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[<0>] 0xffffffffffffffff
The waiting writer locks out all subsequent readers to avoid lock
starvation, and several threads can be seen hanging like this:
[<0>] call_rwsem_down_read_failed+0x14/0x30
[<0>] proc_pid_cmdline_read+0xa0/0x480
[<0>] __vfs_read+0x23/0x140
[<0>] vfs_read+0x87/0x130
[<0>] SyS_read+0x42/0x90
[<0>] do_syscall_64+0x5b/0x100
[<0>] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[<0>] 0xffffffffffffffff
To fix this, do what we do for cache read faults already: drop the
mmap_sem before calling into anything IO bound, in this case the
balance_dirty_pages() function, and return VM_FAULT_RETRY.
Link: http://lkml.kernel.org/r/20190924194238.GA29030@xxxxxxxxxxx
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Josef Bacik <josef@xxxxxxxxxxxxxx>
Cc: Hillf Danton <hdanton@xxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 21 ---------------------
mm/internal.h | 21 +++++++++++++++++++++
mm/memory.c | 38 +++++++++++++++++++++++++++-----------
3 files changed, 48 insertions(+), 32 deletions(-)
--- a/mm/filemap.c~mm-drop-mmap_sem-before-calling-balance_dirty_pages-in-write-fault
+++ a/mm/filemap.c
@@ -2328,27 +2328,6 @@ EXPORT_SYMBOL(generic_file_read_iter);
#ifdef CONFIG_MMU
#define MMAP_LOTSAMISS (100)
-static struct file *maybe_unlock_mmap_for_io(struct vm_fault *vmf,
- struct file *fpin)
-{
- int flags = vmf->flags;
-
- if (fpin)
- return fpin;
-
- /*
- * FAULT_FLAG_RETRY_NOWAIT means we don't want to wait on page locks or
- * anything, so we only pin the file and drop the mmap_sem if only
- * FAULT_FLAG_ALLOW_RETRY is set.
- */
- if ((flags & (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT)) ==
- FAULT_FLAG_ALLOW_RETRY) {
- fpin = get_file(vmf->vma->vm_file);
- up_read(&vmf->vma->vm_mm->mmap_sem);
- }
- return fpin;
-}
-
/*
* lock_page_maybe_drop_mmap - lock the page, possibly dropping the mmap_sem
* @vmf - the vm_fault for this fault.
--- a/mm/internal.h~mm-drop-mmap_sem-before-calling-balance_dirty_pages-in-write-fault
+++ a/mm/internal.h
@@ -362,6 +362,27 @@ vma_address(struct page *page, struct vm
return max(start, vma->vm_start);
}
+static inline struct file *maybe_unlock_mmap_for_io(struct vm_fault *vmf,
+ struct file *fpin)
+{
+ int flags = vmf->flags;
+
+ if (fpin)
+ return fpin;
+
+ /*
+ * FAULT_FLAG_RETRY_NOWAIT means we don't want to wait on page locks or
+ * anything, so we only pin the file and drop the mmap_sem if only
+ * FAULT_FLAG_ALLOW_RETRY is set.
+ */
+ if ((flags & (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT)) ==
+ FAULT_FLAG_ALLOW_RETRY) {
+ fpin = get_file(vmf->vma->vm_file);
+ up_read(&vmf->vma->vm_mm->mmap_sem);
+ }
+ return fpin;
+}
+
#else /* !CONFIG_MMU */
static inline void clear_page_mlock(struct page *page) { }
static inline void mlock_vma_page(struct page *page) { }
--- a/mm/memory.c~mm-drop-mmap_sem-before-calling-balance_dirty_pages-in-write-fault
+++ a/mm/memory.c
@@ -2227,10 +2227,11 @@ static vm_fault_t do_page_mkwrite(struct
*
* The function expects the page to be locked and unlocks it.
*/
-static void fault_dirty_shared_page(struct vm_area_struct *vma,
- struct page *page)
+static vm_fault_t fault_dirty_shared_page(struct vm_fault *vmf)
{
+ struct vm_area_struct *vma = vmf->vma;
struct address_space *mapping;
+ struct page *page = vmf->page;
bool dirtied;
bool page_mkwrite = vma->vm_ops && vma->vm_ops->page_mkwrite;
@@ -2245,16 +2246,30 @@ static void fault_dirty_shared_page(stru
mapping = page_rmapping(page);
unlock_page(page);
+ if (!page_mkwrite)
+ file_update_time(vma->vm_file);
+
+ /*
+ * Throttle page dirtying rate down to writeback speed.
+ *
+ * mapping may be NULL here because some device drivers do not
+ * set page.mapping but still dirty their pages
+ *
+ * Drop the mmap_sem before waiting on IO, if we can. The file
+ * is pinning the mapping, as per above.
+ */
if ((dirtied || page_mkwrite) && mapping) {
- /*
- * Some device drivers do not set page.mapping
- * but still dirty their pages
- */
+ struct file *fpin;
+
+ fpin = maybe_unlock_mmap_for_io(vmf, NULL);
balance_dirty_pages_ratelimited(mapping);
+ if (fpin) {
+ fput(fpin);
+ return VM_FAULT_RETRY;
+ }
}
- if (!page_mkwrite)
- file_update_time(vma->vm_file);
+ return 0;
}
/*
@@ -2497,6 +2512,7 @@ static vm_fault_t wp_page_shared(struct
__releases(vmf->ptl)
{
struct vm_area_struct *vma = vmf->vma;
+ vm_fault_t ret = VM_FAULT_WRITE;
get_page(vmf->page);
@@ -2520,10 +2536,10 @@ static vm_fault_t wp_page_shared(struct
wp_page_reuse(vmf);
lock_page(vmf->page);
}
- fault_dirty_shared_page(vma, vmf->page);
+ ret |= fault_dirty_shared_page(vmf);
put_page(vmf->page);
- return VM_FAULT_WRITE;
+ return ret;
}
/*
@@ -3567,7 +3583,7 @@ static vm_fault_t do_shared_fault(struct
return ret;
}
- fault_dirty_shared_page(vma, vmf->page);
+ ret |= fault_dirty_shared_page(vmf);
return ret;
}
_
Patches currently in -mm which might be from hannes@xxxxxxxxxxx are
mm-drop-mmap_sem-before-calling-balance_dirty_pages-in-write-fault.patch
