PFStat. Global notes

Transcription

1 PFStat Global notes

2 Counts expand_stack returns in case of error, so the stack_low count needed to be inside transparent huge page, 2 cases : There is no PMD, we should create a transparent one (There is a PMD, which is transparent) File : filemap_fault Fault_alloced_page : not counted. Only one group managed it.

3 Reset pfstat pfstat->stack_low = 0; pfstat->transparent_hugepage_fault = 0; pfstat->anonymous_fault = 0; pfstat->file_fault = 0; pfstat->swapped_back = 0; pfstat->copy_on_write = 0; pfstat->fault_alloced_page = 0; memset(pfstat,0,sizeof(struct pfstat));

4 Shell $? and $! can be anywhere in the command line /bin/echo $? have to work /bin/echo "$?" may work (in a normal shell it would be replaced) my_command & Usually displays something

5 Read vs Mmap Global notes

6 Read vs Mmap In order of importance Theoretical study Complete pro's and con's, including usage Study the impact of file size There is a graphical way to represent the difference The total amount of ram is taken into consideration / swapping is reviewed The methodology makes sense There is actually a memory access after the mmap (or nothing is read) Cache is flushed, or taken into account Study the impact of the access pattern Random vs Sequential Study the impact of the operation size (read of 1byte, 1k, 1M?) Bonuses : Impact of huge pages Other fancy ideas

7 Next TP Topics of interest?

8 File Systems UniqueFS : Unique File File System Importance : 2 14/05/ h59

9 UniqueFS Implemented as a module, using a good Kconfig entry in a good location Supports only one file ; no sub-folders, etc. Just a unique file (no sym link or hard link) Able to change the name of the file, max 32 char Able to list the (only) root folder containing the only file or not The file is deletable The file is seekable The file is mmapable (2 points) In the normal step, the file content is stored in memory, hence it is a virtual file system, as there is no block device backing it

10 Documentation /doc/documentation/filesystems/vfs.txt Lot of similarities with ramfs Though do not copy cut it, stay minimal and implement only the needed functions for UniqueFS.

11 Linux VFS Register a file system with register_filesystem (in your module init) takes a struct file_system_type struct file_system_type uniquefs_fs_type = {.owner = THIS_MODULE,.name = "uniquefs",.mount = uniquefs_mount, //To implement, mount a device to a location. This function return a "dentry", a directory. The root directory..fs_flags = FS_USERNS_MOUNT, //From fs.h:1861 Allow user. Real FS backed by a device use FS_REQUIRES_DEV };

12 Mount Wrap a call to mount_nodev (virtual FS) or mount_bdev (block-devices FS) struct dentry *uniquefs_mount(struct file_system_type *fs_type, int flags, const char *dev_name, void *data) { return mount_nodev(fs_type, flags, data, uniquefs_fill_super); }; Uniquefs_fill_super must fill the superblock.

13 Fill super block Super-block is stored on disk (synchronized) for non-virtual FS and contain all informations about the file system int uniquefs_fill_super(struct super_block *sb, void *data, int silent) { sb->s_blocksize = PAGE_CACHE_SIZE; sb->s_blocksize_bits = PAGE_CACHE_SHIFT; sb->s_op = &uniquefs_ops; inode = //Create the root DIRECTORY inode sb->s_root = d_make_root(inode); }

14 Inode creation Regular file inode->i_op = &uniquefs_file_inode_operations; inode->i_fop = &uniquefs_file_operations; Directory : inode->i_op = &uniquefs_dir_inode_operations; inode->i_fop = &simple_dir_operations; //Generic dir

15 uniquefs_file_operations Tells how to operate on an open file (read, ) const struct file_operations uniquefs_file_operations = {.read = uniquefs_read //.write = //.mmap = };

16 uniquefs_file_inode_operations Describe how to manipulate an inode const struct inode_operations uniquefs_file_inode_operations = {.setattr = simple_setattr,.getattr = simple_getattr, }; //For a virtual FS, this is sufficient

17 Extended Perfect virtual UniqueFS : 18/20 (including mmap) Physical UniqueFS (backed by a disk device) : +4 points Shell must be updated to format the partition with "mkfs.uniquefs", the file is not present after format. Be sure 'echo "mkfs.uniquefs /dev/sdxy"./shell" works. If you go for the extended version, please add an empty "extended" file as mounting etc is different Keep a tag of the virtual version of UniqueFS, so if you try the extended version and fail, you can revert to the virtual one...

18 Submission Tar.gz Shell with Makefile in all cases Shell must be fixed with correction mentioned in PFstat correction (rare) Especially : no segfault Linux Patch including previous steps (diff with ) Pfstat does not need to be fixed, but your kernel must compile (...) "extended" file if extended version Report Everything following usual rules (project number, file names, group numbers, etc)