Dymanic memory allocation is not done or checked at compile time, its done at run time, so when a kernel module or any code in kernel request memory thru kmalloc(), kmalloc() first checks if it can find the memory block somwhat greater than the requested memory size, if it is not able to get any memory block of suffient size it returns an error. Once again, I would like to say, all this is done at run time (execution time). It has nothing to do with compilation. Regards, Gaurav. -----Original Message----- From: kernelnewbies-bounce@xxxxxxxxxxxx [mailto:kernelnewbies-bounce@xxxxxxxxxxxx] On Behalf Of Borislav Petkov Sent: Monday, August 02, 2004 2:14 PM To: kernelnewbies@xxxxxxxxxxxx Subject: kmalloc question -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi there people, i only need a confirmation on some unclear issues concerning the following function: <include/linux/slab.h> 77 static inline void *kmalloc(size_t size, int flags) 78 { 79 if (__builtin_constant_p(size)) { 80 int i = 0; 81 #define CACHE(x) \ 82 if (size <= x) \ 83 goto found; \ 84 else \ 85 i++; 86 #include "kmalloc_sizes.h" 87 #undef CACHE 88 { 89 extern void __you_cannot_kmalloc_that_much(void); 90 __you_cannot_kmalloc_that_much(); 91 } 92 found: 93 return kmem_cache_alloc((flags & GFP_DMA) ? 94 malloc_sizes[i].cs_dmacachep : 95 malloc_sizes[i].cs_cachep, flags); 96 } 97 return __kmalloc(size, flags); 98 } I understand that the CACHE macro is used to search the malloc_sizes array to find a slab object that is (size <= x) and if it is found, we jump to the found label where we call kmem_cache_alloc(). After we #undef CACHE, we have a block with that external function that is declared nowhere. After googling a while, I think I know what this does but i'm not sure - when, at compile time, something requests a slab object that is bigger than the alloc'd ones, we break compilation and force the caller to change its call to kmalloc in order to request a more suitable size object. I don't understand the thoughts behind that, though, thus my question. Thanks in advance for your help, Boris. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.5 (GNU/Linux) iD8DBQFBDf64iBySr3Fn37QRAsreAJ4nAZof1ixOM3ZDo2ADIMjgXrYCzACfXBVc VMqT17YfOFPlmPyEXOLjxic= =i6PV -----END PGP SIGNATURE----- -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
