For each physical cluster, there is a straight-forward way of allocating a fixed or variable-sized array to record the corresponding file pages for its decompression if we decide to decompress these pages asynchronously (eg. read-ahead case), however it will take variable-sized 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 to store parts of the array itself in order to minimize the extra memory overhead, thus only a small-sized constant array used for booting the whole array itself up will be needed. Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx> --- fs/erofs/zpvec.h | 159 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 159 insertions(+) create mode 100644 fs/erofs/zpvec.h diff --git a/fs/erofs/zpvec.h b/fs/erofs/zpvec.h new file mode 100644 index 000000000000..bb7689e67836 --- /dev/null +++ b/fs/erofs/zpvec.h @@ -0,0 +1,159 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * linux/fs/erofs/zpvec.h + * + * Copyright (C) 2018 HUAWEI, Inc. + * http://www.huawei.com/ + * Created by Gao Xiang <gaoxiang25@xxxxxxxxxx> + */ +#ifndef __EROFS_FS_ZPVEC_H +#define __EROFS_FS_ZPVEC_H + +#include "tagptr.h" + +/* page type in pagevec for decompress 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) + 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 int nr) +{ + unsigned int index; + + /* keep away from occupied pages */ + if (ctor->next) + return ctor->next; + + for (index = 0; index < nr; ++index) { + const erofs_vtptr_t t = ctor->pages[index]; + const unsigned int tags = tagptr_unfold_tags(t); + + if (tags == Z_EROFS_PAGE_TYPE_EXCLUSIVE) + return tagptr_unfold_ptr(t); + } + DBG_BUGON(nr >= ctor->nr); + 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 int nr, + erofs_vtptr_t *pages, + unsigned int 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_enqueue(struct z_erofs_pagevec_ctor *ctor, + struct page *page, + enum z_erofs_page_type type, + bool *occupied) +{ + *occupied = false; + if (unlikely(!ctor->next && 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_dequeue(struct z_erofs_pagevec_ctor *ctor, + enum z_erofs_page_type *type) +{ + erofs_vtptr_t t; + + if (unlikely(ctor->index >= ctor->nr)) { + DBG_BUGON(!ctor->next); + 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 + -- 2.17.1
