Peter, Thats' fine. I have already gone through those articles, and user space techniques are fine with me. But here I have to do it ( flush the cache ) from kernel module, so I have to do all the things that kernel does when it get argument 3 into /proc/sys/vm/dropcaches.
Now again drop_caches_sysctl_handler function accepts lots of argument and its not defined in .h file, so what I have to do is, I have to pass those arguments to this function and include it in my module by exporting this function. This is a bit of cumbersome and I really don't know weather it will work or not !!!!! Just asking, if I export only drop_pagecache function and add it in my module, it will work or not. Or, any other better way to handle this case from kernel module ???? Thanks & Best Regards, Krishna On Sat, Jul 18, 2009 at 11:12 AM, Peter Teoh <htmldevelo...@gmail.com>wrote: > 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<erkris...@gmail.com> 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 <htmldevelo...@gmail.com> > 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 >
