linux-imx

// SPDX-License-Identifier: GPL-2.0

#include <linux/mm.h>

#include <linux/mmzone.h>

#include <linux/memblock.h>

#include <linux/page_ext.h>

#include <linux/memory.h>

#include <linux/vmalloc.h>

#include <linux/kmemleak.h>

#include <linux/page_owner.h>

#include <linux/page_idle.h>

​

/*

 * struct page extension

 *

 * This is the feature to manage memory for extended data per page.

 *

 * Until now, we must modify struct page itself to store extra data per page.

 * This requires rebuilding the kernel and it is really time consuming process.

 * And, sometimes, rebuild is impossible due to third party module dependency.

 * At last, enlarging struct page could cause un-wanted system behaviour change.

 *

 * This feature is intended to overcome above mentioned problems. This feature

 * allocates memory for extended data per page in certain place rather than

 * the struct page itself. This memory can be accessed by the accessor

 * functions provided by this code. During the boot process, it checks whether

 * allocation of huge chunk of memory is needed or not. If not, it avoids

 * allocating memory at all. With this advantage, we can include this feature

 * into the kernel in default and can avoid rebuild and solve related problems.

 *

 * To help these things to work well, there are two callbacks for clients. One

 * is the need callback which is mandatory if user wants to avoid useless

 * memory allocation at boot-time. The other is optional, init callback, which

 * is used to do proper initialization after memory is allocated.

 *

 * The need callback is used to decide whether extended memory allocation is

 * needed or not. Sometimes users want to deactivate some features in this

 * boot and extra memory would be unneccessary. In this case, to avoid

 * allocating huge chunk of memory, each clients represent their need of

 * extra memory through the need callback. If one of the need callbacks

 * returns true, it means that someone needs extra memory so that

 * page extension core should allocates memory for page extension. If

 * none of need callbacks return true, memory isn't needed at all in this boot

 * and page extension core can skip to allocate memory. As result,

 * none of memory is wasted.

 *

 * When need callback returns true, page_ext checks if there is a request for

 * extra memory through size in struct page_ext_operations. If it is non-zero,

 * extra space is allocated for each page_ext entry and offset is returned to

 * user through offset in struct page_ext_operations.

 *

 * The init callback is used to do proper initialization after page extension

 * is completely initialized. In sparse memory system, extra memory is

 * allocated some time later than memmap is allocated. In other words, lifetime

 * of memory for page extension isn't same with memmap for struct page.

 * Therefore, clients can't store extra data until page extension is

 * initialized, even if pages are allocated and used freely. This could

 * cause inadequate state of extra data per page, so, to prevent it, client

 * can utilize this callback to initialize the state of it correctly.

 */

​

static struct page_ext_operations *page_ext_ops[] = {

#ifdef CONFIG_DEBUG_PAGEALLOC

    &debug_guardpage_ops,