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Date: Fri, 6 Apr 2018 10:25:25 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Sayan Ghosh <sgdgp.2014@...il.com>, linux-ext4@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org,
niloy ganguly <ganguly.niloy@...il.com>,
Madhumita Mallick <madhu.cse.ju@...il.com>,
"Bhattacharya, Suparna" <suparna.bhattacharya@....com>,
"Bharde, Madhumita" <madhumita.bharde@....com>
Subject: Re: [Patch 3/4] Memory-mapped writing and reading of a graded file
spanning over two media types
On 04/06/2018 04:41 AM, Sayan Ghosh wrote:
> The patch is on top of Linux Kernel 4.7.2.
>
> Signed-off-by: Sayan Ghosh <sgdgp.2014@...il.com>
> ---
> fs/ext4/file.c | 178 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 174 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index df44c87..368cf53 100755
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -298,6 +298,164 @@ static const struct vm_operations_struct
> ext4_file_vm_ops = {
> .page_mkwrite = ext4_page_mkwrite,
> };
>
> +/*
> + * This function is the fault function for our case to
> + * redirect the high grade blocks through DAX path (since the
> + * higher tier we chose is Persistent Memory) and the lower
> + * grade blocks via the normal ext4 fault.
> + * Some parts of the code are copied from ext4_dax_fault.
> + * The parts where the redirection is done is added by additional
> + * comments.
> + */
> +static int graded_ext4_fault(struct vm_area_struct *vma, struct vm_fault *vmf){
Put '{' on separate line.
> + int result;
> + sector_t block;
> + handle_t *handle = NULL;
> + struct file *file = vma->vm_file;
> + struct address_space *mapping = file->f_mapping;
> + struct inode *inode = file_inode(vma->vm_file);
> + struct super_block *sb = inode->i_sb;
> + bool write = vmf->flags & FAULT_FLAG_WRITE;
Indentation. (many)
> +
> + struct grade_struct *grade_array = NULL;
> + unsigned long long total;
> + if (is_file_graded(inode)){
> + total = read_count_xattr(inode);
> + grade_array = (struct grade_struct
> *)kmalloc(total*sizeof(struct grade_struct), GFP_USER);
> + read_grade_xattr(inode,grade_array);
> + }
> +
> + block = (sector_t)vmf->pgoff << (PAGE_SHIFT - mapping->host->i_blkbits);
> + if (write) {
> + sb_start_pagefault(sb);
> + file_update_time(vma->vm_file);
> + down_read(&EXT4_I(inode)->i_mmap_sem);
> + handle = ext4_journal_start_sb(sb, EXT4_HT_WRITE_PAGE,
> + EXT4_DATA_TRANS_BLOCKS(sb));
> + } else
> + down_read(&EXT4_I(inode)->i_mmap_sem);
> +
> + if (IS_ERR(handle))
> + result = VM_FAULT_SIGBUS;
> + else
> + {
> + if(write){
if (write) {
> + unsigned long long temp;
> + if(find_grade(grade_array,total,block,&temp) == 1){
if ( 1) {
> + result = __dax_fault(vma, vmf, ext4_dax_get_block);
> + }
> + else if(find_grade(grade_array,total,block,&temp) == 0){
same.
> + result = ext4_filemap_fault(vma,vmf);
> + }
> + }
> + else{
else {
> + /*
> + * Here the higher graded blocks are redirected via DAX path
> + * since we consider Persistent Memory as higher tier.
> + *
> + * ** TODO **
> + * To take care of the case when the higher tier is not
> + * persistent memory (can be HDD-SSD combination), a check
> + * of the same needs to be provided before re-direction.
> + */
> + unsigned long long temp;
> + if(find_grade(grade_array,total,block,&temp) == 1){
> + result = __dax_fault(vma, vmf, ext4_dax_get_block);
> + }
> + else if(find_grade(grade_array,total,block,&temp) == 0){
> + result = ext4_filemap_fault(vma,vmf);
> + }
> + }
> + }
> + out:
> + if (write) {
> + if (!IS_ERR(handle))
> + ext4_journal_stop(handle);
> + up_read(&EXT4_I(inode)->i_mmap_sem);
> + sb_end_pagefault(sb);
> + } else
> + up_read(&EXT4_I(inode)->i_mmap_sem);
> +
> + return result;
> +}
> +
> +/*
> + * This is the new page write function for our scenario.
> + * This also takes care of the grade and redirects
> + * through the correct path, DAX for higer tier
> + * (Persistent Memory) and ext4 path for lower tier.
> + * To take care of the cases when the higher tier
> + * is not Persistent Memory a TODO has been added
> + */
> +static int graded_ext4_mkwrite(struct vm_area_struct *vma, struct
> vm_fault *vmf){
{ on separate line.
> + int result;
> + sector_t block;
> + handle_t *handle = NULL;
> + struct file *file = vma->vm_file;
> + struct address_space *mapping = file->f_mapping;
> + struct inode *inode = file_inode(vma->vm_file);
> + struct super_block *sb = inode->i_sb;
> + bool write = vmf->flags & FAULT_FLAG_WRITE;
> + block = (sector_t)vmf->pgoff << (PAGE_SHIFT - mapping->host->i_blkbits);
> +
> + struct grade_struct *grade_array = NULL;
> + unsigned long long total;
> + if (is_file_graded(inode)){
> + total = read_count_xattr(inode);
> + grade_array = (struct grade_struct
> *)kmalloc(total*sizeof(struct grade_struct), GFP_USER);
> + read_grade_xattr(inode,grade_array);
> + }
> +
> + if (write) {
> + sb_start_pagefault(sb);
> + file_update_time(vma->vm_file);
> + down_read(&EXT4_I(inode)->i_mmap_sem);
> + handle = ext4_journal_start_sb(sb, EXT4_HT_WRITE_PAGE,
> + EXT4_DATA_TRANS_BLOCKS(sb));
> + } else
> + down_read(&EXT4_I(inode)->i_mmap_sem);
> +
> + if (IS_ERR(handle))
> + result = VM_FAULT_SIGBUS;
> + else{
else {
> + /*
> + * Here the higher graded blocks are redirected via DAX path
> + * since we consider Persistent Memory as higher tier.
> + *
> + * ** TODO **
> + * To take care of the case when the higher tier is not
> + * persistent memory (can be HDD-SSD combination), a check
> + * of the same needs to be provided before re-direction.
> + */
> + unsigned long long temp;
> + if(find_grade(grade_array,total,block,&temp)==1){
> + result = __dax_fault(vma, vmf, ext4_dax_get_block);
> + }
> + else if(find_grade(grade_array,total,block,&temp)==0){
> + filemap_map_pages(vma,vmf);
> + result = ext4_page_mkwrite(vma,vmf);
> + }
> + }
> + if (write) {
> + if (!IS_ERR(handle))
> + ext4_journal_stop(handle);
> + up_read(&EXT4_I(inode)->i_mmap_sem);
> + sb_end_pagefault(sb);
> + } else
> + up_read(&EXT4_I(inode)->i_mmap_sem);
> +
> + return result;
> +}
> +
> +/*
> + * New function pointers for page fault handling and page writes.
> + */
> +static const struct vm_operations_struct graded_ext4_vm_ops = {
> + .fault = graded_ext4_fault,
> + .page_mkwrite = graded_ext4_mkwrite,
> +
> +};
> +
> static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
> {
> struct inode *inode = file->f_mapping->host;
> @@ -310,11 +468,23 @@ static int ext4_file_mmap(struct file *file,
> struct vm_area_struct *vma)
> return -ENOKEY;
> }
> file_accessed(file);
> - if (IS_DAX(file_inode(file))) {
> - vma->vm_ops = &ext4_dax_vm_ops;
> +
> + /*
> + * For graded file new function pointers for
> + * fault and page write are assigned.
> + */
> + if(is_file_graded(file_inode(file))){
if ( ))) {
> + vma->vm_ops = &graded_ext4_vm_ops;
> vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE;
> - } else {
> - vma->vm_ops = &ext4_file_vm_ops;
> + }
> + else{
else {
> + if (IS_DAX(file_inode(file))) {
> + vma->vm_ops = &ext4_dax_vm_ops;
> + vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE;
> + }
> + else {
> + vma->vm_ops = &ext4_file_vm_ops;
> + }
> }
> return 0;
> }
>
>
--
~Randy
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