On Thu, 2006-08-17 at 12:29 +0530, Abu M. Muttalib wrote: > Hi, > > In an application I am freeing some memory address, earlier reserved with > malloc. > > I have put prints in remove_vm_struct() function in ./mm/mmap.c. For few > calls to free(), there is no corresponding call to remove_vm_struct(). I am > not able to understand why the user space call to free() is not propagated > to kernel, where in the remove_vm_strcut() function should get called. Hi, there is 2 parts to this question first of all, glibc malloc doesn't always use mmap for it's allocations, it's a split between the brk() area and mmap() depending on the size of the allocation. (>= 128Kb uses mmap, smaller uses brk(). brk using allocations will not end up in remove_vm_struct at all) second of all, glibc delays freeing of some memory (in the brk() area) to optimize for cases of frequent malloc/free operations, so that it doesn't have to go to the kernel all the time (and a free would imply a cross cpu TLB invalidate which is *expensive*, so batching those up is a really good thing for performance) I hope this answer helps you... it's probably worth reading the malloc/malloc.c code in the glibc code tree, this behavior is documented there... Greetings, Arjan van de Ven -- if you want to mail me at work (you don't), use arjan (at) linux.intel.com - To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.linux-learn.org/faqs
