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    SubjectRe: [PATCH][1/2]page_fault retry with NOPAGE_RETRY
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    On Thu, Apr 9, 2009 at 12:47 AM, Wu Fengguang <fengguang.wu@intel.com> 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@intel.com>
    >
    >> Signed-off-by: Ying Han <yinghan@google.com>
    >> Mike Waychison <mikew@google.com>
    >>
    >> 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?
    >
    >> + 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++;
    >
    > 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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