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pmm: add priority access for paging
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@sparchatus
sparchatus committed Dec 5, 2024
1 parent d01825b commit 60e488b
Showing 1 changed file with 52 additions and 44 deletions.
96 changes: 52 additions & 44 deletions mm/pmm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -48,19 +48,21 @@ static list_head_t busy_frames[MAX_PAGE_ORDER + 1];
(MIN_FREE_FRAMES_THRESHOLD + MIN_NUM_4K_FRAMES + (MAX_PAGE_ORDER - PAGE_ORDER_4K))
static size_t frames_count[MAX_PAGE_ORDER + 1];

static bool refilling;
static spinlock_t lock = SPINLOCK_INIT;

static bool refilling;
static spinlock_t priority_lock = SPINLOCK_INIT;

static void try_create_4k_frames(void);

static void spin_lock_norefill() {
static void spin_lock_standard() {
spin_lock(&lock);
spin_lock(&priority_lock);
}

while (refilling) {
spin_unlock(&lock);
/* TODO: some backoff would be nice here... */
spin_lock(&lock);
}
static void spin_unlock_standard() {
spin_unlock(&priority_lock);
spin_unlock(&lock);
}

void display_frames_count(void) {
Expand Down Expand Up @@ -129,12 +131,16 @@ static frames_array_t *_new_frames_array(bool from_paging) {
/* switch to special refilling mode to avoid deadlock with paging */
ASSERT(!refilling);
refilling = true;

/* only paging will be allowed to take the lock for writing while refilling */
spin_unlock(&lock);
spin_unlock(&priority_lock);
array = vmap_frame_refill(mfn_to_virt_map(frame->mfn), frame->mfn, from_paging);
spin_lock(&lock);
spin_lock(&priority_lock);

/* switch back to normal mode */
ASSERT(refilling);
refilling = false;

if (!array)
goto error;
}
Expand Down Expand Up @@ -458,31 +464,31 @@ static frame_t *_find_mfn_frame(list_head_t *list, mfn_t mfn, unsigned int order
frame_t *find_free_mfn_frame(mfn_t mfn, unsigned int order) {
frame_t *frame;

spin_lock(&lock);
spin_lock_standard();
frame = _find_mfn_frame(free_frames, mfn, order);
spin_unlock(&lock);
spin_unlock_standard();

return frame;
}

frame_t *find_busy_mfn_frame(mfn_t mfn, unsigned int order) {
frame_t *frame;

spin_lock(&lock);
spin_lock_standard();
frame = _find_mfn_frame(busy_frames, mfn, order);
spin_unlock(&lock);
spin_unlock_standard();

return frame;
}

frame_t *find_mfn_frame(mfn_t mfn, unsigned int order) {
frame_t *frame;

spin_lock(&lock);
spin_lock_standard();
frame = _find_mfn_frame(busy_frames, mfn, order);
if (!frame)
frame = _find_mfn_frame(free_frames, mfn, order);
spin_unlock(&lock);
spin_unlock_standard();

return frame;
}
Expand All @@ -503,31 +509,31 @@ static frame_t *_find_paddr_frame(list_head_t *list, paddr_t paddr) {
frame_t *find_free_paddr_frame(paddr_t paddr) {
frame_t *frame;

spin_lock(&lock);
spin_lock_standard();
frame = _find_paddr_frame(free_frames, paddr);
spin_unlock(&lock);
spin_unlock_standard();

return frame;
}

frame_t *find_busy_paddr_frame(paddr_t paddr) {
frame_t *frame;

spin_lock(&lock);
spin_lock_standard();
frame = _find_paddr_frame(busy_frames, paddr);
spin_unlock(&lock);
spin_unlock_standard();

return frame;
}

frame_t *find_paddr_frame(paddr_t paddr) {
frame_t *frame;

spin_lock(&lock);
spin_lock_standard();
frame = _find_paddr_frame(busy_frames, paddr);
if (!frame)
frame = _find_paddr_frame(free_frames, paddr);
spin_unlock(&lock);
spin_unlock_standard();

return frame;
}
Expand Down Expand Up @@ -631,20 +637,20 @@ static void try_create_4k_frames(void) {
* This function does not split larger frames.
*/
frame_t *get_free_frames_cond(free_frames_cond_t cb) {
spin_lock_norefill();
spin_lock_standard();
try_create_4k_frames();
for_each_order (order) {
frame_t *frame;

list_for_each_entry (frame, &free_frames[order], list) {
if (cb(frame)) {
reserve_frame(frame);
spin_unlock(&lock);
spin_unlock_standard();
return frame;
}
}
}
spin_unlock(&lock);
spin_unlock_standard();

return NULL;
}
Expand All @@ -655,22 +661,22 @@ frame_t *get_free_frames(unsigned int order) {
if (order > MAX_PAGE_ORDER)
return NULL;

spin_lock_norefill();
spin_lock_standard();
if (order == PAGE_ORDER_4K)
try_create_4k_frames();

while (list_is_empty(&free_frames[order])) {
BUG_ON(order == PAGE_ORDER_4K);
frame = find_larger_frame(free_frames, order);
if (!frame) {
spin_unlock(&lock);
spin_unlock_standard();
return NULL;
}
split_frame(frame);
}

frame = reserve_frame(get_first_frame(free_frames, order));
spin_unlock(&lock);
spin_unlock_standard();

return frame;
}
Expand All @@ -680,7 +686,7 @@ void put_free_frames(mfn_t mfn, unsigned int order) {

ASSERT(order <= MAX_PAGE_ORDER);

spin_lock(&lock);
spin_lock_standard();
frame = _find_mfn_frame(busy_frames, mfn, order);
if (!frame) {
warning("PMM: unable to find frame: %lx, order: %u among busy frames", mfn,
Expand All @@ -692,20 +698,7 @@ void put_free_frames(mfn_t mfn, unsigned int order) {
merge_frames(frame);

unlock:
spin_unlock(&lock);
}

frame_t *get_free_frame_norefill(void) {
frame_t *frame;

spin_lock(&lock);
frame = reserve_frame(get_first_frame(free_frames, PAGE_ORDER_4K));
spin_unlock(&lock);

/* we ran out of reserved frames. increase MIN_NUM_4K_FRAMES */
BUG_ON(!frame);

return frame;
spin_unlock_standard();
}

void map_frames_array(void) {
Expand All @@ -720,8 +713,23 @@ void map_frames_array(void) {
}
}

/* functions for paging to avoid deadlocks */

frame_t *get_free_frame_norefill(void) {
frame_t *frame;

spin_lock(&priority_lock);
frame = reserve_frame(get_first_frame(free_frames, PAGE_ORDER_4K));
spin_unlock(&priority_lock);

/* we ran out of reserved frames. increase MIN_NUM_4K_FRAMES */
BUG_ON(!frame);

return frame;
}

void refill_from_paging(void) {
spin_lock(&lock);
spin_lock(&priority_lock);

/* if a refill is already active then they are responsible */
if (!refilling) {
Expand All @@ -734,5 +742,5 @@ void refill_from_paging(void) {
try_create_4k_frames();
}

spin_unlock(&lock);
spin_unlock(&priority_lock);
}

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