Hi, In the file mm/bootmem.c, there is a declaration: bootmem_data_t bootmem_node_data[MAX_NUMNODES] __initdata; (Please see: http://lxr.linux.no/linux+v2.6.33/mm/bootmem.c#L35) The above declaration allocates space at compile time for an array of bootmem_data_t type inside the .init.data section of the vmlinux. Each member of this array is further pointing to a bitmap which is allocated at run-time. (Please see the node_bootmem_map field inside bootmem_data_t structure - http://lxr.linux.no/linux+v2.6.33/include/linux/bootmem.h#L37) Now, when the kernel function alloc_bootmem() (or its variants alloc_bootmem_low() , alloc_bootmem_pages() or alloc_bootmem_low_pages()) are used, it results in invocation of alloc_bootmem_core() which seems to be scanning this bitmap to set the bits inside it, depending upon the size argument passed to it. Also, as I understand from my perusal of the kernel code, all the code and data marked with __initdata qualifier are freed by the kernel, when free_initmem() is invoked. Now I have following queries: 1. I fail to understand why is this declaration marked with __initdata qualifier? Does it mean that this array bootmem_node_data would not be used by the kernel anytime after booting is complete? 2. The usage of __initdata qualifier with bootmem_node_data variable also implies that alloc_bootmem() and free_bootmem( along with their variants) can be used only before free_initmem() is invoked by the kernel. Is there any such implicit or explicit dependency or relation between the invocation order of alloc_bootmem() and free_initmem()? I am saying this because, alloc_bootmem() seems to be scanning the associated bitmap of bootmem_data_t and free_bootmem() seems to be again scanning the bitmap. 3. Also, What would happen in case, the associated data structure (i.e bootmem_node_data) itself is freed by the kernel during free_initmem() first, and then some piece of code has still not called its free_bootmem() ? Would it not result in lost references to the bootmem’s bitmap. How does kernel ensure that these kind of lost references to the bitmap does not happen? I think I have explained my doubts clearly. Some of the understanding of kernel concepts might not be totally correct here. Thanks to everyone for their help in understanding this. With Regards, Himanshu Aggarwal -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
