Commit 5eb20ec3 authored by Gao Xiang's avatar Gao Xiang Committed by Greg Kroah-Hartman

staging: erofs: introduce pagevec for unzip subsystem

For each compressed cluster, there is a straight-forward
way of allocating a fixed or variable-sized (for VLE) array
to record the corresponding file pages for its decompression
if we decide to decompress these pages asynchronously (eg.
read-ahead case), however it could take much extra on-heap
memory compared with traditional uncompressed filesystems.

This patch introduces a pagevec solution to reuse some
allocated file page in the time-sharing approach storing
parts of the array itself in order to minimize the extra
memory overhead, thus only a constant and small-sized array
used for booting the whole array itself up will be needed.
Signed-off-by: default avatarGao Xiang <gaoxiang25@huawei.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent b8b58b32
/* SPDX-License-Identifier: GPL-2.0
*
* linux/drivers/staging/erofs/unzip_pagevec.h
*
* Copyright (C) 2018 HUAWEI, Inc.
* http://www.huawei.com/
* Created by Gao Xiang <gaoxiang25@huawei.com>
*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file COPYING in the main directory of the Linux
* distribution for more details.
*/
#ifndef __EROFS_UNZIP_PAGEVEC_H
#define __EROFS_UNZIP_PAGEVEC_H
#include <linux/tagptr.h>
/* page type in pagevec for unzip subsystem */
enum z_erofs_page_type {
/* including Z_EROFS_VLE_PAGE_TAIL_EXCLUSIVE */
Z_EROFS_PAGE_TYPE_EXCLUSIVE,
Z_EROFS_VLE_PAGE_TYPE_TAIL_SHARED,
Z_EROFS_VLE_PAGE_TYPE_HEAD,
Z_EROFS_VLE_PAGE_TYPE_MAX
};
extern void __compiletime_error("Z_EROFS_PAGE_TYPE_EXCLUSIVE != 0")
__bad_page_type_exclusive(void);
/* pagevec tagged pointer */
typedef tagptr2_t erofs_vtptr_t;
/* pagevec collector */
struct z_erofs_pagevec_ctor {
struct page *curr, *next;
erofs_vtptr_t *pages;
unsigned int nr, index;
};
static inline void z_erofs_pagevec_ctor_exit(struct z_erofs_pagevec_ctor *ctor,
bool atomic)
{
if (ctor->curr == NULL)
return;
if (atomic)
kunmap_atomic(ctor->pages);
else
kunmap(ctor->curr);
}
static inline struct page *
z_erofs_pagevec_ctor_next_page(struct z_erofs_pagevec_ctor *ctor,
unsigned nr)
{
unsigned index;
/* keep away from occupied pages */
if (ctor->next != NULL)
return ctor->next;
for (index = 0; index < nr; ++index) {
const erofs_vtptr_t t = ctor->pages[index];
const unsigned tags = tagptr_unfold_tags(t);
if (tags == Z_EROFS_PAGE_TYPE_EXCLUSIVE)
return tagptr_unfold_ptr(t);
}
if (unlikely(nr >= ctor->nr))
BUG();
return NULL;
}
static inline void
z_erofs_pagevec_ctor_pagedown(struct z_erofs_pagevec_ctor *ctor,
bool atomic)
{
struct page *next = z_erofs_pagevec_ctor_next_page(ctor, ctor->nr);
z_erofs_pagevec_ctor_exit(ctor, atomic);
ctor->curr = next;
ctor->next = NULL;
ctor->pages = atomic ?
kmap_atomic(ctor->curr) : kmap(ctor->curr);
ctor->nr = PAGE_SIZE / sizeof(struct page *);
ctor->index = 0;
}
static inline void z_erofs_pagevec_ctor_init(struct z_erofs_pagevec_ctor *ctor,
unsigned nr,
erofs_vtptr_t *pages, unsigned i)
{
ctor->nr = nr;
ctor->curr = ctor->next = NULL;
ctor->pages = pages;
if (i >= nr) {
i -= nr;
z_erofs_pagevec_ctor_pagedown(ctor, false);
while (i > ctor->nr) {
i -= ctor->nr;
z_erofs_pagevec_ctor_pagedown(ctor, false);
}
}
ctor->next = z_erofs_pagevec_ctor_next_page(ctor, i);
ctor->index = i;
}
static inline bool
z_erofs_pagevec_ctor_enqueue(struct z_erofs_pagevec_ctor *ctor,
struct page *page,
enum z_erofs_page_type type,
bool *occupied)
{
*occupied = false;
if (unlikely(ctor->next == NULL && type))
if (ctor->index + 1 == ctor->nr)
return false;
if (unlikely(ctor->index >= ctor->nr))
z_erofs_pagevec_ctor_pagedown(ctor, false);
/* exclusive page type must be 0 */
if (Z_EROFS_PAGE_TYPE_EXCLUSIVE != (uintptr_t)NULL)
__bad_page_type_exclusive();
/* should remind that collector->next never equal to 1, 2 */
if (type == (uintptr_t)ctor->next) {
ctor->next = page;
*occupied = true;
}
ctor->pages[ctor->index++] =
tagptr_fold(erofs_vtptr_t, page, type);
return true;
}
static inline struct page *
z_erofs_pagevec_ctor_dequeue(struct z_erofs_pagevec_ctor *ctor,
enum z_erofs_page_type *type)
{
erofs_vtptr_t t;
if (unlikely(ctor->index >= ctor->nr)) {
BUG_ON(ctor->next == NULL);
z_erofs_pagevec_ctor_pagedown(ctor, true);
}
t = ctor->pages[ctor->index];
*type = tagptr_unfold_tags(t);
/* should remind that collector->next never equal to 1, 2 */
if (*type == (uintptr_t)ctor->next)
ctor->next = tagptr_unfold_ptr(t);
ctor->pages[ctor->index++] =
tagptr_fold(erofs_vtptr_t, NULL, 0);
return tagptr_unfold_ptr(t);
}
#endif
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