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: Gao Xiang <gaoxiang25@huawei.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Gao Xiang
Greg Kroah-Hartman
parent
b8b58b3280
commit
5eb20ec3e5
172
drivers/staging/erofs/unzip_pagevec.h
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172
drivers/staging/erofs/unzip_pagevec.h
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/* SPDX-License-Identifier: GPL-2.0
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*
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* linux/drivers/staging/erofs/unzip_pagevec.h
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*
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* Copyright (C) 2018 HUAWEI, Inc.
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* http://www.huawei.com/
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* Created by Gao Xiang <gaoxiang25@huawei.com>
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*
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* This file is subject to the terms and conditions of the GNU General Public
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* License. See the file COPYING in the main directory of the Linux
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* distribution for more details.
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*/
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#ifndef __EROFS_UNZIP_PAGEVEC_H
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#define __EROFS_UNZIP_PAGEVEC_H
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#include <linux/tagptr.h>
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/* page type in pagevec for unzip subsystem */
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enum z_erofs_page_type {
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/* including Z_EROFS_VLE_PAGE_TAIL_EXCLUSIVE */
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Z_EROFS_PAGE_TYPE_EXCLUSIVE,
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Z_EROFS_VLE_PAGE_TYPE_TAIL_SHARED,
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Z_EROFS_VLE_PAGE_TYPE_HEAD,
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Z_EROFS_VLE_PAGE_TYPE_MAX
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};
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extern void __compiletime_error("Z_EROFS_PAGE_TYPE_EXCLUSIVE != 0")
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__bad_page_type_exclusive(void);
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/* pagevec tagged pointer */
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typedef tagptr2_t erofs_vtptr_t;
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/* pagevec collector */
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struct z_erofs_pagevec_ctor {
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struct page *curr, *next;
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erofs_vtptr_t *pages;
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unsigned int nr, index;
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};
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static inline void z_erofs_pagevec_ctor_exit(struct z_erofs_pagevec_ctor *ctor,
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bool atomic)
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{
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if (ctor->curr == NULL)
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return;
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if (atomic)
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kunmap_atomic(ctor->pages);
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else
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kunmap(ctor->curr);
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}
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static inline struct page *
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z_erofs_pagevec_ctor_next_page(struct z_erofs_pagevec_ctor *ctor,
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unsigned nr)
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{
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unsigned index;
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/* keep away from occupied pages */
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if (ctor->next != NULL)
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return ctor->next;
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for (index = 0; index < nr; ++index) {
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const erofs_vtptr_t t = ctor->pages[index];
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const unsigned tags = tagptr_unfold_tags(t);
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if (tags == Z_EROFS_PAGE_TYPE_EXCLUSIVE)
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return tagptr_unfold_ptr(t);
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}
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if (unlikely(nr >= ctor->nr))
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BUG();
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return NULL;
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}
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static inline void
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z_erofs_pagevec_ctor_pagedown(struct z_erofs_pagevec_ctor *ctor,
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bool atomic)
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{
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struct page *next = z_erofs_pagevec_ctor_next_page(ctor, ctor->nr);
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z_erofs_pagevec_ctor_exit(ctor, atomic);
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ctor->curr = next;
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ctor->next = NULL;
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ctor->pages = atomic ?
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kmap_atomic(ctor->curr) : kmap(ctor->curr);
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ctor->nr = PAGE_SIZE / sizeof(struct page *);
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ctor->index = 0;
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}
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static inline void z_erofs_pagevec_ctor_init(struct z_erofs_pagevec_ctor *ctor,
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unsigned nr,
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erofs_vtptr_t *pages, unsigned i)
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{
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ctor->nr = nr;
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ctor->curr = ctor->next = NULL;
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ctor->pages = pages;
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if (i >= nr) {
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i -= nr;
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z_erofs_pagevec_ctor_pagedown(ctor, false);
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while (i > ctor->nr) {
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i -= ctor->nr;
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z_erofs_pagevec_ctor_pagedown(ctor, false);
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}
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}
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ctor->next = z_erofs_pagevec_ctor_next_page(ctor, i);
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ctor->index = i;
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}
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static inline bool
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z_erofs_pagevec_ctor_enqueue(struct z_erofs_pagevec_ctor *ctor,
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struct page *page,
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enum z_erofs_page_type type,
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bool *occupied)
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{
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*occupied = false;
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if (unlikely(ctor->next == NULL && type))
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if (ctor->index + 1 == ctor->nr)
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return false;
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if (unlikely(ctor->index >= ctor->nr))
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z_erofs_pagevec_ctor_pagedown(ctor, false);
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/* exclusive page type must be 0 */
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if (Z_EROFS_PAGE_TYPE_EXCLUSIVE != (uintptr_t)NULL)
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__bad_page_type_exclusive();
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/* should remind that collector->next never equal to 1, 2 */
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if (type == (uintptr_t)ctor->next) {
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ctor->next = page;
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*occupied = true;
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}
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ctor->pages[ctor->index++] =
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tagptr_fold(erofs_vtptr_t, page, type);
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return true;
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}
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static inline struct page *
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z_erofs_pagevec_ctor_dequeue(struct z_erofs_pagevec_ctor *ctor,
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enum z_erofs_page_type *type)
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{
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erofs_vtptr_t t;
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if (unlikely(ctor->index >= ctor->nr)) {
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BUG_ON(ctor->next == NULL);
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z_erofs_pagevec_ctor_pagedown(ctor, true);
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}
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t = ctor->pages[ctor->index];
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*type = tagptr_unfold_tags(t);
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/* should remind that collector->next never equal to 1, 2 */
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if (*type == (uintptr_t)ctor->next)
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ctor->next = tagptr_unfold_ptr(t);
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ctor->pages[ctor->index++] =
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tagptr_fold(erofs_vtptr_t, NULL, 0);
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return tagptr_unfold_ptr(t);
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}
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#endif
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