Re: [PATCH][1/2]page_fault retry with NOPAGE_RETRY

From: Wu Fengguang
Date: Thu Apr 09 2009 - 20:25:52 EST

On Fri, Apr 10, 2009 at 12:21:25AM +0800, Ying Han wrote:
> On Thu, Apr 9, 2009 at 12:47 AM, Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> > On Thu, Apr 09, 2009 at 04:02:35AM +0800, Ying Han wrote:
> >> support for FAULT_FLAG_RETRY with no user change:
> >
> > A better changelog is desired, otherwise:
> >
> > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> >
> >> Signed-off-by: Ying Han <yinghan@xxxxxxxxxx>
> >> Mike Waychison <mikew@xxxxxxxxxx>
> >>
> >> include/linux/fs.h | 2 +-
> >> include/linux/mm.h | 2 +
> >> mm/filemap.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++--
> >> mm/memory.c | 33 +++++++++++++++++------
> >>
> >>
> >> diff --git a/include/linux/fs.h b/include/linux/fs.h
> >> index 4a853ef..29c2c39 100644
> >> --- a/include/linux/fs.h
> >> +++ b/include/linux/fs.h
> >> @@ -793,7 +793,7 @@ struct file_ra_state {
> >> there are only # of pages ahead */
> >>
> >> unsigned int ra_pages; /* Maximum readahead window */
> >> - int mmap_miss; /* Cache miss stat for mmap accesses */
> >> + unsigned int mmap_miss; /* Cache miss stat for mmap accesses */
> >> loff_t prev_pos; /* Cache last read() position */
> >> };
> >>
> >> diff --git a/include/linux/mm.h b/include/linux/mm.h
> >> index ffee2f7..5a134a9 100644
> >> --- a/include/linux/mm.h
> >> +++ b/include/linux/mm.h
> >> @@ -144,6 +144,7 @@ extern pgprot_t protection_map[16];
> >>
> >> #define FAULT_FLAG_WRITE 0x01 /* Fault was a write access */
> >> #define FAULT_FLAG_NONLINEAR 0x02 /* Fault was via a nonlinear mapping */
> >> +#define FAULT_FLAG_RETRY 0x04 /* Retry major fault */
> >>
> >>
> >> /*
> >> @@ -690,6 +691,7 @@ static inline int page_mapped(struct page *page)
> >>
> >> #define VM_FAULT_MINOR 0 /* For backwards compat. Remove me quickly. */
> >>
> >> +#define VM_FAULT_RETRY 0x0010
> >> #define VM_FAULT_OOM 0x0001
> >> #define VM_FAULT_SIGBUS 0x0002
> >> #define VM_FAULT_MAJOR 0x0004
> >
> > Why not append VM_FAULT_RETRY here, and indent the _OOM line?
> >
> >> diff --git a/mm/filemap.c b/mm/filemap.c
> >> index f3e5f89..6eb7c36 100644
> >> --- a/mm/filemap.c
> >> +++ b/mm/filemap.c
> >> @@ -714,6 +714,58 @@ repeat:
> >> EXPORT_SYMBOL(find_lock_page);
> >>
> >> /**
> >> + * find_lock_page_retry - locate, pin and lock a pagecache page
> >> + * @mapping: the address_space to search
> >> + * @offset: the page index
> >> + * @vma: vma in which the fault was taken
> >> + * @ppage: zero if page not present, otherwise point to the page in pagecache
> >> + * @retry: 1 indicate caller tolerate a retry.
> >> + *
> >> + * If retry flag is on, and page is already locked by someone else, return
> >> + * a hint of retry and leave *ppage untouched.
> >> + *
> >> + * Return *ppage==NULL if page is not in pagecache. Otherwise return *ppage
> >> + * points to the page in the pagecache with ret=VM_FAULT_RETRY indicate a
> >> + * hint to caller for retry, or ret=0 which means page is succefully
> >> + * locked.
> >> + */
> >> +unsigned find_lock_page_retry(struct address_space *mapping, pgoff_t offset,
> >> + struct vm_area_struct *vma, struct page **ppage,
> >> + int retry)
> >> +{
> >> + unsigned int ret = 0;
> >> + struct page *page;
> >> +
> >> +repeat:
> >> + page = find_get_page(mapping, offset);
> >> + if (page) {
> >> + if (!retry)
> >> + lock_page(page);
> >> + else {
> >> + if (!trylock_page(page)) {
> >> + struct mm_struct *mm = vma->vm_mm;
> >> +
> >> + up_read(&mm->mmap_sem);
> >> + wait_on_page_locked(page);
> >> + down_read(&mm->mmap_sem);
> >> +
> >> + page_cache_release(page);
> >> + return VM_FAULT_RETRY;
> >> + }
> >> + }
> >> + if (unlikely(page->mapping != mapping)) {
> >> + unlock_page(page);
> >> + page_cache_release(page);
> >> + goto repeat;
> >> + }
> >> + VM_BUG_ON(page->index != offset);
> >> + }
> >> + *ppage = page;
> >> + return ret;
> >> +}
> >> +EXPORT_SYMBOL(find_lock_page_retry);
> >> +
> >> +/**
> >> * find_or_create_page - locate or add a pagecache page
> >> * @mapping: the page's address_space
> >> * @index: the page's index into the mapping
> >> @@ -1444,6 +1496,8 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_
> >> pgoff_t size;
> >> int did_readaround = 0;
> >> int ret = 0;
> >> + int retry_flag = vmf->flags & FAULT_FLAG_RETRY;
> >> + int retry_ret;
> >>
> >> size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
> >> if (vmf->pgoff >= size)
> >> @@ -1458,6 +1512,7 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_
> >> */
> >> retry_find:
> >> page = find_lock_page(mapping, vmf->pgoff);
> >> +
> >> /*
> >> * For sequential accesses, we use the generic readahead logic.
> >> */
> >> @@ -1465,7 +1520,13 @@ retry_find:
> >> if (!page) {
> >> page_cache_sync_readahead(mapping, ra, file,
> >> vmf->pgoff, 1);
> >> - page = find_lock_page(mapping, vmf->pgoff);
> >> + retry_ret = find_lock_page_retry(mapping, vmf->pgoff,
> >> + vma, &page, retry_flag);
> >> + if (retry_ret == VM_FAULT_RETRY) {
> >> + /* counteract the followed retry hit */
> >> + ra->mmap_miss++;
> >
> > Please don't relocate the comment...because that will break my
> > following patches(mainly Linus' filemap cleanups), which will
> > _heavily_ rework these chunks anyway. And make a hard time for Andrew
> > to merge them.
>
> then how you force the 80 character lines?

The above line will be removed by my following patch, and...

> >
> >> + return retry_ret;
> >> + }
> >
> >> if (!page)
> >> goto no_cached_page;
> >> }
> >> @@ -1504,7 +1565,14 @@ retry_find:
> >> start = vmf->pgoff - ra_pages / 2;
> >> do_page_cache_readahead(mapping, file, start, ra_pages);
> >> }
> >> - page = find_lock_page(mapping, vmf->pgoff);
> >> +retry_find_retry:
> >> + retry_ret = find_lock_page_retry(mapping, vmf->pgoff,
> >> + vma, &page, retry_flag);
> >> + if (retry_ret == VM_FAULT_RETRY) {
> >> + /* counteract the followed retry hit */
> >> + ra->mmap_miss++;
> >

...this line can have the comment within 80 column, and will be kept
by my patch.

Thanks,
Fengguang


> > ditto
> >
> > Thanks,
> > Fengguang
> >
> >> + return retry_ret;
> >> + }
> >> if (!page)
> >> goto no_cached_page;
> >> }
> >> @@ -1548,7 +1616,7 @@ no_cached_page:
> >> * meantime, we'll just come back here and read it again.
> >> */
> >> if (error >= 0)
> >> - goto retry_find;
> >> + goto retry_find_retry;
> >>
> >> /*
> >> * An error return from page_cache_read can result if the
> >> diff --git a/mm/memory.c b/mm/memory.c
> >> index 164951c..5e215c9 100644
> >> --- a/mm/memory.c
> >> +++ b/mm/memory.c
> >> @@ -2467,6 +2467,13 @@ static int __do_fault(struct mm_struct *mm, struct vm_a
> >> vmf.page = NULL;
> >>
> >> ret = vma->vm_ops->fault(vma, &vmf);
> >> +
> >> + /* page may be available, but we have to restart the process
> >> + * because mmap_sem was dropped during the ->fault
> >> + */
> >> + if (ret & VM_FAULT_RETRY)
> >> + return ret;
> >> +
> >> if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
> >> return ret;
> >>
> >> @@ -2611,8 +2618,10 @@ static int do_linear_fault(struct mm_struct *mm, struct
> >> {
> >> pgoff_t pgoff = (((address & PAGE_MASK)
> >> - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
> >> - unsigned int flags = (write_access ? FAULT_FLAG_WRITE : 0);
> >> + int write = write_access & ~FAULT_FLAG_RETRY;
> >> + unsigned int flags = (write ? FAULT_FLAG_WRITE : 0);
> >>
> >> + flags |= (write_access & FAULT_FLAG_RETRY);
> >> pte_unmap(page_table);
> >> return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
> >> }
> >> @@ -2726,26 +2735,32 @@ int handle_mm_fault(struct mm_struct *mm, struct vm_ar
> >> pud_t *pud;
> >> pmd_t *pmd;
> >> pte_t *pte;
> >> + int ret;
> >>
> >> __set_current_state(TASK_RUNNING);
> >>
> >> - count_vm_event(PGFAULT);
> >> -
> >> - if (unlikely(is_vm_hugetlb_page(vma)))
> >> - return hugetlb_fault(mm, vma, address, write_access);
> >> + if (unlikely(is_vm_hugetlb_page(vma))) {
> >> + ret = hugetlb_fault(mm, vma, address, write_access);
> >> + goto out;
> >> + }
> >>
> >> + ret = VM_FAULT_OOM;
> >> pgd = pgd_offset(mm, address);
> >> pud = pud_alloc(mm, pgd, address);
> >> if (!pud)
> >> - return VM_FAULT_OOM;
> >> + goto out;
> >> pmd = pmd_alloc(mm, pud, address);
> >> if (!pmd)
> >> - return VM_FAULT_OOM;
> >> + goto out;
> >> pte = pte_alloc_map(mm, pmd, address);
> >> if (!pte)
> >> - return VM_FAULT_OOM;
> >> + goto out;
> >>
> >> - return handle_pte_fault(mm, vma, address, pte, pmd, write_access);
> >> + ret = handle_pte_fault(mm, vma, address, pte, pmd, write_access);
> >> +out:
> >> + if (!(ret & VM_FAULT_RETRY))
> >> + count_vm_event(PGFAULT);
> >> + return ret;
> >> }
> >>
> >> #ifndef __PAGETABLE_PUD_FOLDED
> >
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