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// SPDX-License-Identifier: GPL-2.0-only
/* Page fragment allocator
*
* Page Fragment:
* An arbitrary-length arbitrary-offset area of memory which resides within a
* 0 or higher order page. Multiple fragments within that page are
* individually refcounted, in the page's reference counter.
*
* The page_frag functions provide a simple allocation framework for page
* fragments. This is used by the network stack and network device drivers to
* provide a backing region of memory for use as either an sk_buff->head, or to
* be used in the "frags" portion of skb_shared_info.
*/
#include <linux/build_bug.h>
#include <linux/export.h>
#include <linux/gfp_types.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/page_frag_cache.h>
#include "internal.h"
static unsigned long encoded_page_create(struct page *page, unsigned int order,
bool pfmemalloc)
{
BUILD_BUG_ON(PAGE_FRAG_CACHE_MAX_ORDER > PAGE_FRAG_CACHE_ORDER_MASK);
BUILD_BUG_ON(PAGE_FRAG_CACHE_PFMEMALLOC_BIT >= PAGE_SIZE);
return (unsigned long)page_address(page) |
(order & PAGE_FRAG_CACHE_ORDER_MASK) |
((unsigned long)pfmemalloc * PAGE_FRAG_CACHE_PFMEMALLOC_BIT);
}
static unsigned long encoded_page_decode_order(unsigned long encoded_page)
{
return encoded_page & PAGE_FRAG_CACHE_ORDER_MASK;
}
static void *encoded_page_decode_virt(unsigned long encoded_page)
{
return (void *)(encoded_page & PAGE_MASK);
}
static struct page *encoded_page_decode_page(unsigned long encoded_page)
{
return virt_to_page((void *)encoded_page);
}
static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
gfp_t gfp_mask)
{
unsigned long order = PAGE_FRAG_CACHE_MAX_ORDER;
struct page *page = NULL;
gfp_t gfp = gfp_mask;
#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
gfp_mask = (gfp_mask & ~__GFP_DIRECT_RECLAIM) | __GFP_COMP |
__GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC;
page = __alloc_pages(gfp_mask, PAGE_FRAG_CACHE_MAX_ORDER,
numa_mem_id(), NULL);
#endif
if (unlikely(!page)) {
page = __alloc_pages(gfp, 0, numa_mem_id(), NULL);
order = 0;
}
nc->encoded_page = page ?
encoded_page_create(page, order, page_is_pfmemalloc(page)) : 0;
return page;
}
void page_frag_cache_drain(struct page_frag_cache *nc)
{
if (!nc->encoded_page)
return;
__page_frag_cache_drain(encoded_page_decode_page(nc->encoded_page),
nc->pagecnt_bias);
nc->encoded_page = 0;
}
EXPORT_SYMBOL(page_frag_cache_drain);
void __page_frag_cache_drain(struct page *page, unsigned int count)
{
VM_BUG_ON_PAGE(page_ref_count(page) == 0, page);
if (page_ref_sub_and_test(page, count))
free_unref_page(page, compound_order(page));
}
EXPORT_SYMBOL(__page_frag_cache_drain);
void *__page_frag_alloc_align(struct page_frag_cache *nc,
unsigned int fragsz, gfp_t gfp_mask,
unsigned int align_mask)
{
unsigned long encoded_page = nc->encoded_page;
unsigned int size, offset;
struct page *page;
if (unlikely(!encoded_page)) {
refill:
page = __page_frag_cache_refill(nc, gfp_mask);
if (!page)
return NULL;
encoded_page = nc->encoded_page;
/* Even if we own the page, we do not use atomic_set().
* This would break get_page_unless_zero() users.
*/
page_ref_add(page, PAGE_FRAG_CACHE_MAX_SIZE);
/* reset page count bias and offset to start of new frag */
nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
nc->offset = 0;
}
size = PAGE_SIZE << encoded_page_decode_order(encoded_page);
offset = __ALIGN_KERNEL_MASK(nc->offset, ~align_mask);
if (unlikely(offset + fragsz > size)) {
if (unlikely(fragsz > PAGE_SIZE)) {
/*
* The caller is trying to allocate a fragment
* with fragsz > PAGE_SIZE but the cache isn't big
* enough to satisfy the request, this may
* happen in low memory conditions.
* We don't release the cache page because
* it could make memory pressure worse
* so we simply return NULL here.
*/
return NULL;
}
page = encoded_page_decode_page(encoded_page);
if (!page_ref_sub_and_test(page, nc->pagecnt_bias))
goto refill;
if (unlikely(encoded_page_decode_pfmemalloc(encoded_page))) {
free_unref_page(page,
encoded_page_decode_order(encoded_page));
goto refill;
}
/* OK, page count is 0, we can safely set it */
set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1);
/* reset page count bias and offset to start of new frag */
nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
offset = 0;
}
nc->pagecnt_bias--;
nc->offset = offset + fragsz;
return encoded_page_decode_virt(encoded_page) + offset;
}
EXPORT_SYMBOL(__page_frag_alloc_align);
/*
* Frees a page fragment allocated out of either a compound or order 0 page.
*/
void page_frag_free(void *addr)
{
struct page *page = virt_to_head_page(addr);
if (unlikely(put_page_testzero(page)))
free_unref_page(page, compound_order(page));
}
EXPORT_SYMBOL(page_frag_free);
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