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While the maximum size of each ramdisk is defined either as a module parameter, or compile time default, it's impossible to know how many pages have currently been allocated by each ram%d device, since they're allocated when used and never freed. This patch creates a new directory at this location: /sys/kernel/debug/ramdisk_pages/ which will contain a file named "ram%d" for each instantiated ramdisk on the system. The file is read-only, and read() will output the number of pages currently held by that ramdisk. We lose track how much memory a ramdisk is using as pages once used are simply recycled but never freed. In instances where we exhaust the size of the ramdisk with a file that exceeds it, encounter ENOSPC and delete the file for mitigation; df would show decrease in used and increase in available blocks but the since we have touched all pages, the memory footprint of the ramdisk does not reflect the blocks used/available count ... [root@localhost ~]# mkfs.ext2 /dev/ram15 mke2fs 1.45.6 (20-Mar-2020) Creating filesystem with 4096 1k blocks and 1024 inodes [root@localhost ~]# mount /dev/ram15 /mnt/ram15/ [root@localhost ~]# cat /sys/kernel/debug/ramdisk_pages/ram15 58 [root@kerneltest008.06.prn3 ~]# df /dev/ram15 Filesystem 1K-blocks Used Available Use% Mounted on /dev/ram15 3963 31 3728 1% /mnt/ram15 [root@kerneltest008.06.prn3 ~]# dd if=/dev/urandom of=/mnt/ram15/test2 bs=1M count=5 dd: error writing '/mnt/ram15/test2': No space left on device 4+0 records in 3+0 records out 4005888 bytes (4.0 MB, 3.8 MiB) copied, 0.0446614 s, 89.7 MB/s [root@kerneltest008.06.prn3 ~]# df /mnt/ram15/ Filesystem 1K-blocks Used Available Use% Mounted on /dev/ram15 3963 3960 0 100% /mnt/ram15 [root@kerneltest008.06.prn3 ~]# cat /sys/kernel/debug/ramdisk_pages/ram15 1024 [root@kerneltest008.06.prn3 ~]# rm /mnt/ram15/test2 rm: remove regular file '/mnt/ram15/test2'? y [root@kerneltest008.06.prn3 /var]# df /dev/ram15 Filesystem 1K-blocks Used Available Use% Mounted on /dev/ram15 3963 31 3728 1% /mnt/ram15 # Acutal memory footprint [root@kerneltest008.06.prn3 /var]# cat /sys/kernel/debug/ramdisk_pages/ram15 1024 ... This debugfs counter will always reveal the accurate number of permanently allocated pages to the ramdisk. Signed-off-by: Calvin Owens <calvinowens@fb.com> [cleaned up the !CONFIG_DEBUG_FS case and API changes for HEAD] Signed-off-by: Kyle McMartin <jkkm@fb.com> [rebased] Signed-off-by: Saravanan D <saravanand@fb.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.