one more thing good to know is the importance/reasons for ZONE_HIGHMEM. Whenever process swap between userspace and kernelspace processing, Linux Kernel is designed NOT to do TLB flushing - and this means that the pagetable must not be modified. In 3G/1G memory division, pagetables for these users tasks must exists inside the 1G kernel portion. But of these about 850KB is occupied by the ZONE_NORMAL, and the remaining is used for pagetables and misc structures. To be noted is also that these VMA-mapped memory are always temporary (readup: kmap()). Most the standard kernel functions will automatically use identity-mapped memory, which can access ZONE_NORMAL memory only. Check this out: http://ols.fedoraproject.org/OLS/Reprints-2004/Reprint-Bottomley-OLS2004.pdf On Tue, Mar 3, 2009 at 3:43 PM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote: > - Show quoted text - > On Tue, Mar 3, 2009 at 2:41 PM, NAHieu <nahieu@xxxxxxxxx> wrote: >> On Tue, Mar 3, 2009 at 3:29 PM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote: >>> - Show quoted text - >>> On Tue, Mar 3, 2009 at 11:39 AM, NAHieu <nahieu@xxxxxxxxx> wrote: >>>> On Tue, Mar 3, 2009 at 12:16 PM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote: >>>>> This is the first time I have seen the word "unity-mapping"......if it >>>>> is your invention....congratulations!!!! U have created a new term. >>>> >>>> so you learned a new term today :-). but i agree that it is not >>>> popular, and it confused me at first. >>>> >>>> so the more popular one is "identity mapping", right? >>>> >>>> that is not my term, but somebody else. I read that on internet somewhere ... >>>> >>>>> >>>>> Usually I heard of "identity mapping", "direct mapping", linear >>>>> mapping, vs "non-linear mapping". The formula is basically >>>>> equivalent to __pa(), and all the different variation: __va(), >>>>> virt_to_page(), pfn_to_kaddr() etc. It is all just using a >>>>> straightforward formula. This is because virtual address and >>>>> physical addr are inter-convertible directly in the ZONE_NORMAL range. >>>>> But not in the ZONE_HIGH area. kmalloc() always returned addresses >>>>> in these range. All the confusing API like pud*, pgd*, pmd*() API >>>>> also hinges on this characteristic to convert directly between >>>>> physical and virtual, or to extract out page frame number, PTE etc >>>>> from the virtual/physical addresses. >>>> >>>> OK, so the difference between kmalloc and vmalloc in term of address >>>> they return: >>>> - kmalloc() always return addresses in ZONE_NORMAL >>>> - vmalloc() always returns addresses in ZONE_HIGH >>>> >>>> Could you confirm that is correct? >>> >>> to the best of my knowledge....i think yes. >>> >>>> >>>> So my question now is: what is ZONE_NORMAL range? I mean from what >>>> address to what address? >>>> >>> >>> eh.....check header file definition......it varies from arch to arch, >>> and may be modified at bootup time via some parameter as well. but >>> don't have to know either - cannot find any reason for that. can i >>> know why did u ask? >> >> I am working on a tool to analyze the kernel memory, so I need to >> understand how kernel manages and layouts its memory. >> > > analyze the memory for what? patterns of allocation? patterns of > API usages? or performance analysis of different APIs used? > > > -- > Regards, > Peter Teoh > -- 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
