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page cache: proper truncation

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Matheus
2026-08-20 22:36:38 -03:00
parent 31f9ae17cf
commit 7217a1e258
9 changed files with 170 additions and 58 deletions
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kernel-src/mm/page.c
+42 -13
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@@ -124,6 +124,18 @@ static void internal_hold(page_t *page) {
}
}
static bool try_page_reclaim(page_t *page) {
int flags = __atomic_load_n(&page->flags, __ATOMIC_RELAXED);
for (;;) {
if (flags & PAGE_FLAGS_TRUNCATED)
return false;
if (__atomic_compare_exchange_n(&page->flags, &flags, flags | PAGE_FLAGS_RECLAIMING, true, __ATOMIC_ACQ_REL, __ATOMIC_RELAXED))
return true;
}
}
page_t *mm_get_page(void *address) {
return &pages[((uintptr_t)address / PAGE_SIZE)];
}
@@ -155,6 +167,25 @@ void mm_release_page(void *addr) {
MUTEX_RELEASE(&free_list_mutex);
}
void mm_make_page_anonymous(page_t *page) {
MUTEX_ACQUIRE(&free_list_mutex);
__assert(page->backing);
bool on_standby = page->refcount == 0;
if (on_standby)
remove_from_free_list(page);
page->backing = NULL;
if (on_standby) {
__atomic_or_fetch(&page->flags, PAGE_FLAGS_FREE, __ATOMIC_RELAXED);
insert_in_free_list(page);
}
MUTEX_RELEASE(&free_list_mutex);
}
void mm_unlock_and_release_page(void *addr) {
page_t *page = &pages[(uintptr_t)addr / PAGE_SIZE];
mm_unlock_page(page);
@@ -176,7 +207,6 @@ static void do_alloc(page_t *page) {
}
void *mm_alloc_page(int section) {
retry:
MUTEX_ACQUIRE(&free_list_mutex);
page_t *page = NULL;
@@ -196,23 +226,22 @@ void *mm_alloc_page(int section) {
if (page == NULL) {
for (int i = section; i >= 0; --i) {
page = standby_tails[i];
if (page) {
cache_page = true;
internal_hold(page);
break;
}
while (page && try_page_reclaim(page) == false)
page = page->free_prev;
if (page == NULL)
continue;
cache_page = true;
internal_hold(page);
break;
}
}
MUTEX_RELEASE(&free_list_mutex);
if (cache_page && mm_cache_take_page(page) == EAGAIN) {
// someone already got the page from the cache between us holding it and taking it
mm_release_page(mm_get_page_address(page));
page = NULL;
// retry it from the start, as an anonymous page could have been released while the lock was not held
goto retry;
} else if (cache_page) {
if (cache_page) {
mm_cache_take_page(page);
// we got the page from the cache, all is good and we hold the only reference to it.
// set the refcount to 0, as expected by the do_alloc call
page->refcount = 0;