diff --git a/src/Makefile.build b/src/Makefile.build index 4167f37..4398839 100644 --- a/src/Makefile.build +++ b/src/Makefile.build @@ -62,6 +62,8 @@ userprog_SRC += userprog/gdt.c # GDT initialization. userprog_SRC += userprog/tss.c # TSS management. # Virtual memory code. +vm_SRC += vm/frame.c # Frame table manager. +vm_SRC += vm/page.c # Page table manager. vm_SRC += devices/swap.c # Swap block manager. vm_SRC += vm/stackgrowth.c #vm_SRC = vm/file.c # Some other file. diff --git a/src/threads/init.c b/src/threads/init.c index 2a93d4f..69ac6af 100644 --- a/src/threads/init.c +++ b/src/threads/init.c @@ -32,6 +32,7 @@ #include "tests/threads/tests.h" #endif #ifdef VM +#include "vm/frame.h" #include "devices/swap.h" #endif #ifdef FILESYS @@ -101,6 +102,9 @@ main (void) palloc_init (user_page_limit); malloc_init (); paging_init (); +#ifdef VM + frame_init (); +#endif /* Segmentation. */ #ifdef USERPROG diff --git a/src/userprog/process.c b/src/userprog/process.c index 1f56875..aa5091c 100644 --- a/src/userprog/process.c +++ b/src/userprog/process.c @@ -24,6 +24,9 @@ #include "threads/vaddr.h" #include "threads/synch.h" #include "devices/timer.h" +#ifdef VM +#include "vm/frame.h" +#endif /* Defines the native number of bytes processed by the processor (for the purposes of alignment). */ @@ -113,7 +116,10 @@ process_execute (const char *cmd) return tid; } +static void *get_usr_kpage (enum palloc_flags flags, void *upage); +static void free_usr_kpage (void *kpage); static bool install_page (void *upage, void *kpage, bool writable); + static bool process_init_stack (char *cmd_saveptr, void **esp, char *file_name); static void *push_to_stack (void **esp, void *data, size_t data_size); #define push_var_to_stack(esp, var) (push_to_stack (esp, &var, sizeof (var))) @@ -251,12 +257,13 @@ process_init_stack (char *cmd_saveptr, void **esp, char *file_name) int pages_needed = DIV_CEIL (overflow_bytes, PGSIZE); /* Allocate the pages and map them to the user process. */ + void *upage; + uint8_t *kpage; for (int i = 1; i < pages_needed + 1; i++) { - uint8_t *kpage = palloc_get_page (PAL_USER | PAL_ZERO); - if (!install_page (((uint8_t *) PHYS_BASE) - PGSIZE * (i + 1), - kpage, true)) - return false; + upage = ((uint8_t *) PHYS_BASE) - PGSIZE * (i + 1); + kpage = get_usr_kpage (PAL_ZERO, upage); + if (!install_page (upage, kpage, true)) return false; } } @@ -704,7 +711,7 @@ load_segment (struct file *file, off_t ofs, uint8_t *upage, if (kpage == NULL){ /* Get a new page of memory. */ - kpage = palloc_get_page (PAL_USER); + kpage = get_usr_kpage (0, upage); if (kpage == NULL){ return false; } @@ -712,7 +719,7 @@ load_segment (struct file *file, off_t ofs, uint8_t *upage, /* Add the page to the process's address space. */ if (!install_page (upage, kpage, writable)) { - palloc_free_page (kpage); + free_usr_kpage (kpage); return false; } @@ -746,19 +753,53 @@ setup_stack (void **esp) { uint8_t *kpage; bool success = false; - - kpage = palloc_get_page (PAL_USER | PAL_ZERO); + + void *upage = ((uint8_t *) PHYS_BASE) - PGSIZE; + + kpage = get_usr_kpage (PAL_ZERO, upage); if (kpage != NULL) { - success = install_page (((uint8_t *) PHYS_BASE) - PGSIZE, kpage, true); + success = install_page (upage, kpage, true); if (success) *esp = PHYS_BASE; else - palloc_free_page (kpage); + free_usr_kpage (kpage); } return success; } +/* Claims a page from the user pool for ownership by the current thread + and returns its kernel address, updating the frame table if VM + is enabled. Requires the intended virtual address for where the page + will be installed. */ +static void * +get_usr_kpage (enum palloc_flags flags, void *upage) +{ + void *page; +#ifdef VM + struct thread *t = thread_current (); + if (pagedir_get_page (t->pagedir, upage) != NULL) + return NULL; + else + page = frame_alloc (flags, upage, t); +#else + page = palloc_get_page (flags | PAL_USER); +#endif + return page; +} + +/* Frees a page belonging to a user process given its kernel address, + updating the frame table if VM is enabled. */ +static void +free_usr_kpage (void *kpage) +{ +#ifdef VM + frame_free (kpage); +#else + palloc_free_page (kpage); +#endif +} + /* Adds a mapping from user virtual address UPAGE to kernel virtual address KPAGE to the page table. If WRITABLE is true, the user process may modify the page; diff --git a/src/vm/frame.c b/src/vm/frame.c new file mode 100644 index 0000000..cdb141c --- /dev/null +++ b/src/vm/frame.c @@ -0,0 +1,256 @@ +#include +#include +#include +#include + +#include "frame.h" +#include "page.h" +#include "threads/malloc.h" +#include "threads/vaddr.h" +#include "userprog/pagedir.h" +#include "threads/synch.h" +#include "devices/swap.h" + +/* Hash table that maps every active frame's kernel virtual address + to its corresponding 'frame_metadata'.*/ +struct hash frame_table; + +/* Linked list used to represent the circular queue in the 'clock' + algorithm for page eviction. Iterating from the element that is + currently pointed at by 'next_victim' yields an ordering of the entries + from oldest to newest (in terms of when they were added or checked + for having been referenced by a process). */ +struct list lru_list; + +/* The next element in lru_list to be considered for eviction (oldest added + or referenced page in the circular queue). If this page has has an + 'accessed' bit of 0 when considering eviction, then it will be the next + victim. Otherwise, the next element in the queue is similarly considered. */ +struct list_elem *next_victim = NULL; + +/* Synchronisation variables. */ +/* Protects access to 'lru_list'. */ +struct lock lru_lock; + +struct frame_metadata + { + void *frame; /* The kernel virtual address holding the frame. */ + void *upage; /* The user virtual address pointing to the frame. */ + struct thread *owner; /* Pointer to the thread that owns the frame. */ + struct hash_elem hash_elem; /* Tracks the position of the frame metadata + within 'frame_table', whose key is the + kernel virtual address of the frame. */ + struct list_elem list_elem; /* Tracks the position of the frame metadata + in either the 'active' or 'inactive' list, + so a victim can be chosen for eviction. */ + }; + +hash_hash_func frame_metadata_hash; +hash_less_func frame_metadata_less; + +static struct list_elem *lru_next (struct list_elem *e); +static struct list_elem *lru_prev (struct list_elem *e); +static struct frame_metadata *get_victim (void); + +/* Initialize the frame system by initializing the frame (hash) table with + the frame_metadata hashing and comparison functions, as well as initializing + 'lru_list' and its associated synchronisation primitives. */ +void +frame_init (void) +{ + hash_init (&frame_table, frame_metadata_hash, frame_metadata_less, NULL); + + list_init (&lru_list); + lock_init (&lru_lock); +} + +/* TODO: Consider synchronisation more closely (i.e. just for hash + table). */ +/* Attempt to allocate a frame for a user process, either by direct + allocation of a user page if there is sufficient RAM, or by + evicting a currently active page if memory allocated for user + processes is fulled and storing it in swap. If swap is full in + the former case, panic the kernel. */ +void * +frame_alloc (enum palloc_flags flags, void *upage, struct thread *owner) +{ + struct frame_metadata *frame_metadata; + flags |= PAL_USER; + + lock_acquire (&lru_lock); + void *frame = palloc_get_page (flags); + + /* If a frame couldn't be allocated we must be out of main memory. Thus, + obtain a victim page to replace with our page, and swap the victim + into disk. */ + if (frame == NULL) + { + /* 1. Obtain victim. */ + if (next_victim == NULL) + PANIC ("Couldn't allocate a single page to main memory!\n"); + + struct frame_metadata *victim = get_victim (); + ASSERT (victim != NULL); /* get_victim () should never return null. */ + + /* 2. Swap out victim into disk. */ + size_t swap_slot = swap_out (victim->frame); + page_set_swap (victim->owner, victim->upage, swap_slot); + + /* If zero flag is set, zero out the victim page. */ + if (flags & PAL_ZERO) + memset (victim->frame, 0, PGSIZE); + + /* 3. Indicate that the new frame's metadata will be stored + inside the same structure that stored the victim's metadata. + As both the new frame and the victim frame share the same kernel + virtual address, the hash map need not be updated, and neither + the list_elem value as both share the same lru_list position. */ + frame_metadata = victim; + } + + /* If sufficient main memory allows the frame to be directly allocated, + we must update the frame table with a new entry, and grow lru_list. */ + else + { + /* Must own lru_lock here, as otherwise there is a race condition + with next_victim either being NULL or uninitialized. */ + frame_metadata = malloc (sizeof (struct frame_metadata)); + frame_metadata->frame = frame; + + /* Newly allocated frames are pushed to the back of the circular queue + represented by lru_list. Must explicitly handle the case where the + circular queue is empty (when next_victim == NULL). */ + if (next_victim == NULL) + { + list_push_back (&lru_list, &frame_metadata->list_elem); + next_victim = &frame_metadata->list_elem; + } + else + { + struct list_elem *lru_tail = lru_prev (next_victim); + list_insert (lru_tail, &frame_metadata->list_elem); + } + + hash_insert (&frame_table, &frame_metadata->hash_elem); + } + + frame_metadata->upage = upage; + frame_metadata->owner = owner; + lock_release (&lru_lock); + + return frame_metadata->frame; +} + +/* Attempt to deallocate a frame for a user process by removing it from the + frame table as well as lru_list, and freeing the underlying page + memory & metadata struct. Panics if the frame isn't active in memory. */ +void +frame_free (void *frame) + { + struct frame_metadata key_metadata; + key_metadata.frame = frame; + + struct hash_elem *e = + hash_delete (&frame_table, &key_metadata.hash_elem); + if (e == NULL) PANIC ("Attempted to free a frame at kernel address %p, " + "but this address is not allocated!\n", frame); + + struct frame_metadata *frame_metadata = + hash_entry (e, struct frame_metadata, hash_elem); + + lock_acquire (&lru_lock); + list_remove (&frame_metadata->list_elem); + + /* If we're freeing the frame marked as the next victim, update + next_victim to either be the next least recently used page, or NULL + if no pages are loaded in main memory. */ + if (&frame_metadata->list_elem == next_victim) + { + if (list_empty (&lru_list)) + next_victim = NULL; + else + next_victim = lru_next (next_victim); + } + lock_release (&lru_lock); + + free (frame_metadata); + palloc_free_page (frame); + } + +/* TODO: Account for page aliases when checking accessed bit. */ +/* A pre-condition for calling this function is that the calling thread + owns lru_lock and that lru_list is non-empty. */ +static struct frame_metadata * +get_victim (void) + { + struct list_elem *e = next_victim; + struct frame_metadata *frame_metadata; + uint32_t *pd; + void *upage; + for (;;) + { + frame_metadata = list_entry (e, struct frame_metadata, list_elem); + pd = frame_metadata->owner->pagedir; + upage = frame_metadata->upage; + e = lru_next (e); + + if (!pagedir_is_accessed (pd, upage)) + break; + + pagedir_set_accessed (pd, upage, false); + } + + next_victim = e; + return frame_metadata; + } + +/* Hash function for frame metadata, used for storing entries in the + frame table. */ +unsigned +frame_metadata_hash (const struct hash_elem *e, void *aux UNUSED) + { + struct frame_metadata *frame_metadata = + hash_entry (e, struct frame_metadata, hash_elem); + + return hash_bytes (&frame_metadata->frame, sizeof (frame_metadata->frame)); + } + +/* 'less_func' comparison function for frame metadata, used for comparing + the keys of the frame table. Returns true iff the kernel virtual address + of the first frame is less than that of the second frame. */ +bool +frame_metadata_less (const struct hash_elem *a_, const struct hash_elem *b_, + void *aux UNUSED) + { + struct frame_metadata *a = + hash_entry (a_, struct frame_metadata, hash_elem); + struct frame_metadata *b = + hash_entry (b_, struct frame_metadata, hash_elem); + + return a->frame < b->frame; + } + +/* Returns the next recently used element after the one provided, which + is achieved by iterating through lru_list like a circular queue + (wrapping around the list at the tail). */ +static struct list_elem * +lru_next (struct list_elem *e) +{ + if (!list_empty (&lru_list) && e == list_back (&lru_list)) + return list_front (&lru_list); + + return list_next (e); +} + +/* Returns the previous recently used element after the one provided, which + is achieved by iterating through lru_list like a circular queue + (wrapping around the list at the head). */ +static struct list_elem * +lru_prev (struct list_elem *e) +{ + if (!list_empty (&lru_list) && e == list_front (&lru_list)) + return list_back (&lru_list); + + return list_prev (e); +} + diff --git a/src/vm/frame.h b/src/vm/frame.h new file mode 100644 index 0000000..93081d3 --- /dev/null +++ b/src/vm/frame.h @@ -0,0 +1,11 @@ +#ifndef VM_FRAME_H +#define VM_FRAME_H + +#include "threads/thread.h" +#include "threads/palloc.h" + +void frame_init (void); +void *frame_alloc (enum palloc_flags, void *, struct thread *); +void frame_free (void *frame); + +#endif /* vm/frame.h */ diff --git a/src/vm/page.c b/src/vm/page.c new file mode 100644 index 0000000..8ebc71c --- /dev/null +++ b/src/vm/page.c @@ -0,0 +1,20 @@ +#include "page.h" + +/* Updates the 'owner' thread's page table entry for virtual address 'upage' + to have a present bit of 0 and stores the specified swap slot value in the + entry for later retrieval from disk. */ +void +page_set_swap (struct thread *owner, void *upage, size_t swap_slot) +{ + +} + +/* Given that the page with user address 'upage' owned by 'owner' is flagged + to be in the swap disk via the owner's page table, returns its stored + swap slot. Otherwise panics the kernel. */ +size_t +page_get_swap (struct thread *owner, void *upage) +{ + +} + diff --git a/src/vm/page.h b/src/vm/page.h new file mode 100644 index 0000000..7259ca9 --- /dev/null +++ b/src/vm/page.h @@ -0,0 +1,9 @@ +#ifndef VM_PAGE_H +#define VM_PAGE_H + +#include "threads/thread.h" + +void page_set_swap (struct thread *, void *, size_t); +size_t page_get_swap (struct thread *, void *); + +#endif /* vm/frame.h */