After some extensive reading on the 2. Which consists of two tools;. Swappiness is a property for the Linux kernel that changes the balance between swapping out runtime memory, as opposed to dropping pages from the system page cache. Swappiness can be set to values between 0 and inclusive.
A low value means the kernel will try to avoid swapping as much as possible where a higher value instead will make the kernel aggressively try to use swap space. The default value is 60, and for most desktop systems, setting it to may affect the overall performance, whereas setting it lower even 0 may improve interactivity decreasing response latency. Quoting from vm. Controls the tendency of the kernel to reclaim the memory which is used for caching of directory and inode objects.
By setting swappiness high like , the kernel moves everything it doesn't need to swap, freeing RAM for caching files. I work on a large Java project and every time I run it, it took a lot of RAM and flushed the disk cache, so the next time I compiled the project everything was read from disk again.
By adjusting these two settings, I manage to keep the sources and compiled output cached in RAM, which speeds the process considerably. If you have plenty of memory you can simply read in the files you want to cache with cat or similar. Linux will then do a good job of keeping it around. Linux file caching is very good. If you are seeing disk IO, I would look into your logging configurations.
Many logs get set as unbuffered, in order to guarantee that the latest log information is available in the event of a crash. In systems that have to be fast regardless, use buffered log IO or use a remote log server.
There are various ramfs systems you can use eg, ramfs, tmpfs , but in general if files are actually being read that often, they sit in your filesystem cache.
If your working set of files is larger than your free ram, then files will be cleared out of it - but if your working set is larger than your free ram, there's no way you'll fit it all into a ramdisk either. Check the output of the "free" command in a shell - the value in the last column, under "Cached", is how much of your free ram is being used for filesystem cache.
As for your latter question, ensure that your RAM is sitting on different memory channels so that the processor can fetch the data in parallel. I think this might be better solved at the application level. If you have a specific goal, such as serving web content faster, then you can get improvements form this sort of thing I think.
But your question is general in nature, the Linux memory subsystem is designed to provide the best general use of RAM. The fcoretools package is interesting, I'd be interested in any articles about its application This link talks about the actual system calls used in an application.
Desktop computers eg. It's more focused than the official recommendation of using dd if you just want to read some files. Sometimes I may want to cache files in a certain folder and its subfolders.
I just go to this folder and execute the following:. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?
Learn more. Asked 12 years, 4 months ago. Active 4 years ago. Viewed 79k times. Is it possible to tell the filesystem to always serve certain files out of RAM? Are there any other methods I can use to improve file reading capabilities by use of RAM?
Possible applications here are: Web servers with static files that get read alot Application servers with large libraries Desktop computers with too much RAM Any ideas? What I mean is that it's not being used by applications and I want to control what should be cached in memory. Improve this question. Andrioid Andrioid 2, 2 2 gold badges 19 19 silver badges 21 21 bronze badges. I too am seeking something along these lines. I don't think that general filesystem disk block caching is the answer.
Suppose that I want disk block X to always be cached. Something accesses it, and the kernel caches it. So far so good, but the next process wants block Y, so the kernel discards my block X and caches Y instead. The next process that wants X will have to wait for it to come off the disk; that's what I want to avoid. What I would like and what I think the original poster is after too is to overlay a write-through cache onto a filesystem that will guarantee the files are always — Sacha.
Given that the consensus seems to be that Linux should already be caching frequently-used files for you, I'm wondering if you actually managed to make any improvements using the advice found here. It seems to me that trying to manually control caching might be useful to warm up the cache, but that with the usage pattern you describe "serving the same files all day" , it wouldn't help an already-warmed-up server much, if at all.
You say you're not looking for a hack, but Linux already does what you want to do by default. Did you actually notice any performance improvements? By my experience, Linux cache's the bejeezus out of your filesystem reads.
For clarification, linux does cache files, but the metadata is validated for each file for each request. On spinning rust, on a busy web server with a lot of small files, that can still cause IO contention and prematurely wear out drives. I've done this for a couple decades and my drives don't wear out prematurely. Also my sites withstand heavy burst load much better this way. This helps on anything from the most expensive enterprise hardware to commmodity hardware.
Add a comment. Active Oldest Votes. Improve this answer. Community Bot 1. For future viewers, try to use the vmtouch git repository instead of following the instructions on the linked page. That way you get a makefile and can pull updates. Seems that there's a limit to the size of the file 4GB. Is there any other alternative? Before I get to make a trip there and replace the card and possibly power supply , I want the OS to touch the card sparingly, preferably never.
Let's bring the rest of big-dataset. If only he would accept this as an answer. Do you know if this works with ZFS? Cronjob is a certain inconvenience, but could you comment if there is any disadvantage of using cat file vs.
It will store the computed results temporarily in a period of time. If the report need to reload, results will be loaded from the cache, which results in lowering the load on your database and also the computation of your report. Utimately, it will increase the speed and responsiveness of your report. Keep up your good work! I was impressed by its easiness and powerfulness. This product is a great and amazing. Lew Choy Onn. File Cache Use FileCache to accelerate the response of your report.
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