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Message-Id: <20101011152534.6cf01208.akpm@linux-foundation.org>
Date: Mon, 11 Oct 2010 15:25:34 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Michel Lespinasse <walken@...gle.com>
Cc: Rik van Riel <riel@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
linux-mm@...ck.org, Ying Han <yinghan@...gle.com>,
linux-kernel@...r.kernel.org, Nick Piggin <npiggin@...nel.dk>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/3] Retry page fault when blocking on disk transfer.
On Fri, 8 Oct 2010 18:22:04 -0700
Michel Lespinasse <walken@...gle.com> wrote:
> Second try on adding the VM_FAULT_RETRY functionality to the swap in path.
>
> This proposal would replace [patch 2/3] of this series (the initial
> version of it, which was approved by linus / rik / hpa).
>
> Changes since the approved version:
>
> - split lock_page_or_retry() into an inline function in pagemap.h,
> handling the trylock_page() fast path, and __lock_page_or_retry() in
> filemap.c, handling the blocking path (with or without retry).
>
> - make do_swap_page() call lock_page_or_retry() in place of lock_page(),
> and handle the retry case.
Replacement patches are a bit cruel to people who've already reviewed
the previous version. I always turn them into deltas so I can see what
was changed. It is below.
How well was the new swapin path tested?
include/linux/pagemap.h | 13 +++++++++++++
mm/filemap.c | 35 ++++++++++++++---------------------
mm/memory.c | 7 ++++++-
3 files changed, 33 insertions(+), 22 deletions(-)
diff -puN include/linux/pagemap.h~mm-retry-page-fault-when-blocking-on-disk-transfer-update include/linux/pagemap.h
--- a/include/linux/pagemap.h~mm-retry-page-fault-when-blocking-on-disk-transfer-update
+++ a/include/linux/pagemap.h
@@ -299,6 +299,8 @@ static inline pgoff_t linear_page_index(
extern void __lock_page(struct page *page);
extern int __lock_page_killable(struct page *page);
extern void __lock_page_nosync(struct page *page);
+extern int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
+ unsigned int flags);
extern void unlock_page(struct page *page);
static inline void __set_page_locked(struct page *page)
@@ -351,6 +353,17 @@ static inline void lock_page_nosync(stru
}
/*
+ * lock_page_or_retry - Lock the page, unless this would block and the
+ * caller indicated that it can handle a retry.
+ */
+static inline int lock_page_or_retry(struct page *page, struct mm_struct *mm,
+ unsigned int flags)
+{
+ might_sleep();
+ return trylock_page(page) || __lock_page_or_retry(page, mm, flags);
+}
+
+/*
* This is exported only for wait_on_page_locked/wait_on_page_writeback.
* Never use this directly!
*/
diff -puN mm/filemap.c~mm-retry-page-fault-when-blocking-on-disk-transfer-update mm/filemap.c
--- a/mm/filemap.c~mm-retry-page-fault-when-blocking-on-disk-transfer-update
+++ a/mm/filemap.c
@@ -623,6 +623,19 @@ void __lock_page_nosync(struct page *pag
TASK_UNINTERRUPTIBLE);
}
+int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
+ unsigned int flags)
+{
+ if (!(flags & FAULT_FLAG_ALLOW_RETRY)) {
+ __lock_page(page);
+ return 1;
+ } else {
+ up_read(&mm->mmap_sem);
+ wait_on_page_locked(page);
+ return 0;
+ }
+}
+
/**
* find_get_page - find and get a page reference
* @mapping: the address_space to search
@@ -1512,26 +1525,6 @@ static void do_async_mmap_readahead(stru
page, offset, ra->ra_pages);
}
-/*
- * Lock the page, unless this would block and the caller indicated that it
- * can handle a retry.
- */
-static int lock_page_or_retry(struct page *page,
- struct vm_area_struct *vma, struct vm_fault *vmf)
-{
- if (trylock_page(page))
- return 1;
- if (!(vmf->flags & FAULT_FLAG_ALLOW_RETRY)) {
- __lock_page(page);
- return 1;
- }
-
- up_read(&vma->vm_mm->mmap_sem);
- wait_on_page_locked(page);
- page_cache_release(page);
- return 0;
-}
-
/**
* filemap_fault - read in file data for page fault handling
* @vma: vma in which the fault was taken
@@ -1581,7 +1574,7 @@ retry_find:
goto no_cached_page;
}
- if (!lock_page_or_retry(page, vma, vmf))
+ if (!lock_page_or_retry(page, &vma->vm_mm, vmf->flags))
return ret | VM_FAULT_RETRY;
/* Did it get truncated? */
diff -puN mm/memory.c~mm-retry-page-fault-when-blocking-on-disk-transfer-update mm/memory.c
--- a/mm/memory.c~mm-retry-page-fault-when-blocking-on-disk-transfer-update
+++ a/mm/memory.c
@@ -2627,6 +2627,7 @@ static int do_swap_page(struct mm_struct
struct page *page, *swapcache = NULL;
swp_entry_t entry;
pte_t pte;
+ int locked;
struct mem_cgroup *ptr = NULL;
int exclusive = 0;
int ret = 0;
@@ -2677,8 +2678,12 @@ static int do_swap_page(struct mm_struct
goto out_release;
}
- lock_page(page);
+ locked = lock_page_or_retry(page, mm, flags);
delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
+ if (!locked) {
+ ret |= VM_FAULT_RETRY;
+ goto out_release;
+ }
/*
* Make sure try_to_free_swap or reuse_swap_page or swapoff did not
_
--
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