-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 Hello, I am writing to you because you are listed as Maintainers for the tmpfs file system in the Linux kernel. Recently, I have had a bug in a general purpose application, where it ran out of space in $TMPDIR. As is common, these days, most people vote for /tmp on tmpfs, for obviously good reasons (performance, efficiency etc). http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=831998 On bringing this bug, and the topic of "TMPDIR on tmpfs" on Debian-Devel, there's one comment which wasn't clear to me. Hence this email to you. Even in the description below about tmpfs, it says, "..... to accommodate the files it contains and is able to swap unneeded pages out to swap space." When we say "swap unneeded pages out to swap space", as I understand, what is being referred as "Swappable" here is any process in the kernel's namespace. And not referring to processes associated with /tmp ? Because those mostly will be active processes. The way I observed, it looks like whatever "/tmp on tmpfs" is capped at, from the VFS point of view, is the standard limit for processes accessing files in /tmp. And that file system view and limitations won't change (in effect to other processes being swapped or not). Consider this example: rrs@chutzpah:~$ df -h /tmp/ Filesystem Size Used Avail Use% Mounted on tmpfs 3.7G 3.7M 3.7G 1% /tmp rrs@chutzpah:~$ dd if=/dev/zero of=/tmp/foo.img bs=1M count=4000 dd: error writing '/tmp/foo.img': No space left on device 3691+0 records in 3690+0 records out 3869605888 bytes (3.9 GB, 3.6 GiB) copied, 1.12808 s, 3.4 GB/s rrs@chutzpah:~$ free -m total used free shared buff/cache available Mem: 7387 1882 4396 213 1108 4991 Swap: 8579 109 8470 Here's the description of tmpfs from the latest linux/Documentation/filesystems/tmpfs.txt ============================================================ Tmpfs is a file system which keeps all files in virtual memory. Everything in tmpfs is temporary in the sense that no files will be created on your hard drive. If you unmount a tmpfs instance, everything stored therein is lost. tmpfs puts everything into the kernel internal caches and grows and shrinks to accommodate the files it contains and is able to swap unneeded pages out to swap space. It has maximum size limits which can be adjusted on the fly via 'mount -o remount ...' If you compare it to ramfs (which was the template to create tmpfs) you gain swapping and limit checking. Another similar thing is the RAM disk (/dev/ram*), which simulates a fixed size hard disk in physical RAM, where you have to create an ordinary filesystem on top. Ramdisks cannot swap and you do not have the possibility to resize them. Since tmpfs lives completely in the page cache and on swap, all tmpfs pages will be shown as "Shmem" in /proc/meminfo and "Shared" in free(1). Notice that these counters also include shared memory (shmem, see ipcs(1)). The most reliable way to get the count is using df(1) and du(1). ================================================================ - -- Ritesh Raj Sarraf | http://people.debian.org/~rrs Debian - The Universal Operating System -----BEGIN PGP SIGNATURE----- iQIcBAEBCgAGBQJXlQsoAAoJEKY6WKPy4XVpgCQP/RRaH8IGhUTQdjF8ao00rPXu RPo6ORs03Xn8E6zBP9qZbc2zv0FKTBzM9daTyLDRLzTaF91/eOlR6NQk0Gi6B+66 RO2j7/F4OXs/Axp9Yx8LU0aTUt/A9MV8ugqPaaPRgfgVhdwPVD3zi5pP0uZAwpub fGicjop5vB+lv6PePioDRVOous9eomlI374PF6rP6kE2MSQSqbc+Yw4g8MC7SGZX Xja6OwOvGQTFkbQiT0M4BOjfKEM5S6BI4Vr7R/m4ivkDCj/dJONXQ05Escc8zDuQ yI5Rv39psWDxqTqnSPbENbSNTKw8KbswStgQUN66k/JpRQNNl3C+vLA0a5DWB5pQ q2mSFp66ynGF6DDhlMZOvHpammhecfZpcbFvGBXikuy193SXZfT+k11FJmSSJiVE Q4Tu6JvhADnGpfA07J9PjzV8kRsv9IdAgvFzWUsQeAi8/73ClOl3E7WHkN/zcdvO 5UkOne7h5hJjBNZD3pboQ2To9Wc4qeUWsdC8uHPN0h90fLp3oHA1v4JsraQ/MdbS yDozCgfZ7s/M4/V20OWJ+LlWohdhkeEHKHtZVabPqXpKSpU5UkvWg458Tnlzct85 +/WMVztaF3OKsNb+CiSD0nLuLLi7Gu4TxS6JLZQEaJt/+XET7+mXPjou0g0MVg0X FGEVOJOwFNtQibJY70Qu =lCVO -----END PGP SIGNATURE----- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>