[Minios-devel] Unikraft: Question about binary buddy allocator

[Bruno Alvisio <bruno.alvisio@xxxxxxxxx>]

Hello all,

 

I was reading the binary buddy memory allocator code and I am confused by the meaning of a variable “(struct uk_bbpalloc_memr) memr->nr_pages”. >From its name, it seems to hold the number of pages that belong to the memory region. However, in lib/ukallocbbuddy/bbuddy.c:365 :

 

memr->nr_pages = max - min;

 

which seems to be the actual memory size of the region rather than the number of pages. If my understanding is correct, the following modifications would be needed:

 

diff --git a/lib/ukallocbbuddy/bbuddy.c b/lib/ukallocbbuddy/bbuddy.c

index b830995..c927524 100644

--- a/lib/ukallocbbuddy/bbuddy.c

+++ b/lib/ukallocbbuddy/bbuddy.c

@@ -107,7 +107,7 @@ static inline struct uk_bbpalloc_memr *map_get_memr(struct uk_bbpalloc *b,

         */

        for (memr = b->memr_head; memr != NULL; memr = memr->next) {

                if ((page_num >= memr->first_page)

-                   && (page_num < (memr->first_page + memr->nr_pages)))

+                   && (page_num < (memr->first_page + memr->nr_pages * __PAGE_SIZE)))

                        return memr;

        }

 

@@ -145,7 +145,7 @@ static void map_alloc(struct uk_bbpalloc *b, uintptr_t first_page,

        memr = map_get_memr(b, first_page);

        UK_ASSERT(memr != NULL);

        UK_ASSERT((first_page + nr_pages)

-                 <= (memr->first_page + memr->nr_pages));

+                 <= (memr->first_page + memr->nr_pages * __PAGE_SIZE));

 

        first_page -= memr->first_page;

        curr_idx = first_page / PAGES_PER_MAPWORD;

@@ -362,7 +362,9 @@ static int bbuddy_addmem(struct uk_alloc *a, void *base, size_t len)

         * Initialize region's bitmap

         */

        memr->first_page = min;

-       memr->nr_pages = max - min;

+       int spare = (min - max) % __PAGE_SIZE;

+       UK_ASSERT(spare == 0);

+       memr->nr_pages = (max - min)/__PAGE_SIZE;

        /* add to list */

        memr->next = b->memr_head;

        b->memr_head = memr;

 

 

Let me know if I am missing something. If the change looks correct I can provide a patch.

 

Cheers,

 

Bruno

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