my first attempt at any solution, is to do it in userspace. This article is good: http://aplawrence.com/Linux/buffer_cache.html drop caches is principally used, if u want to remove all existing cache, not flushing it to the storage, so that your next read is guaranteed to be from the storage. but if u want to flush to storage, "sync" is the better option. Many advices are available on the use of drop_cache: http://jons-thoughts.blogspot.com/2007/09/tip-of-day-dropcaches.html http://linux-mm.org/Drop_Caches http://jons-thoughts.blogspot.com/2007/09/tip-of-day-dropcaches.html http://www.linuxreaders.com/tag/drop_caches/ http://ubuntuforums.org/showthread.php?t=1002612 On Sat, Jul 18, 2009 at 12:02 AM, er krishna<erkrishna@xxxxxxxxx> wrote: > Dear Peter, > > Thanks for the great help. > > Just asking, If I have to include this function [ drop_caches_sysctl_handler > ] , then what should I do ? Shall I export it and compile the kernel or is > there any other means to do it. > > Second, I just want to know that there will be lots of hurdels to set the > arguments of above handler, So, if I only export > static void drop_pagecache(void) function in kernel & include this in my > driver, would it work as per the expectation ? > > May be I am wrong, but please correct if the above method need any > modification? > but if u insist on doing it in kernel u HAVE TO WORRY about lots of things: a. what if u are interrupted by hardware/software interrupt? if u cannot tolerate interrupt, then u may need to disable interrupt. but then u have to understand the serious implication of these as well. b. does ANY of the API u are going to call, require any non-blocking condition? or will it result in blocking condition? c. since u are doing it in kernel - how do u ensure that the same is not called by two different CPU at the same time? or, how do u ensure that the SAME cpu don't execute the same function, in a nested manner - assuming interrupt is enabled, and the same function got executed during the 2nd interrupt? lots of small little things to worry about, if not, it will result in kernel crash, or system deadlock.....consequences may result in lost of human life.... for example, even kernel developer had bugs in this API before: http://forum.soft32.com/linux/circular-locking-proc-sys-vm-drop_caches-ftopict340340.html > Thanks & Best regards, > Krishna > > > > > > > On Fri, Jul 17, 2009 at 8:11 PM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote: >> >> sorry....my previous was accidentally sent out halfway...specifically >> detailing on the implementation of drop_caches_sysctl_handler(): >> >> > and reading into the implementation, it just wipe away all the dirty >> > buffer cache (as the name implies). Not really the type of flushing >> > I originally meant - which is to write back the dirty buffer cache to >> > the backing store. >> > >> drop_caches_sysctl_handler()---> >> drop_pagecache()--->drop_pagecache_sb()--->invalidate_mapping_pages(). >> >> where invalidate_mappping_pages() is in mm/truncate.c.....and so on. >> >> and as drop_pagecache_sb() is done for each filesystem's superblock, >> which is why my initial statement is that it is performance-heavy. >> if u know what to flush out, doing it directly will be much better. > > -- Regards, Peter Teoh -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
