ttm_backup.c

  1// SPDX-License-Identifier: MIT
  2/*
  3 * Copyright © 2024 Intel Corporation
  4 */
  5
  6#include <drm/ttm/ttm_backup.h>
  7
  8#include <linux/export.h>
  9#include <linux/page-flags.h>
 10#include <linux/swap.h>
 11
 12/*
 13 * Need to map shmem indices to handle since a handle value
 14 * of 0 means error, following the swp_entry_t convention.
 15 */
 16static unsigned long ttm_backup_shmem_idx_to_handle(pgoff_t idx)
 17{
 18	return (unsigned long)idx + 1;
 19}
 20
 21static pgoff_t ttm_backup_handle_to_shmem_idx(pgoff_t handle)
 22{
 23	return handle - 1;
 24}
 25
 26/**
 27 * ttm_backup_drop() - release memory associated with a handle
 28 * @backup: The struct backup pointer used to obtain the handle
 29 * @handle: The handle obtained from the @backup_page function.
 30 */
 31void ttm_backup_drop(struct file *backup, pgoff_t handle)
 32{
 33	loff_t start = ttm_backup_handle_to_shmem_idx(handle);
 34
 35	start <<= PAGE_SHIFT;
 36	shmem_truncate_range(file_inode(backup), start,
 37			     start + PAGE_SIZE - 1);
 38}
 39
 40/**
 41 * ttm_backup_copy_page() - Copy the contents of a previously backed
 42 * up page
 43 * @backup: The struct backup pointer used to back up the page.
 44 * @dst: The struct page to copy into.
 45 * @handle: The handle returned when the page was backed up.
 46 * @intr: Try to perform waits interruptible or at least killable.
 47 *
 48 * Return: 0 on success, Negative error code on failure, notably
 49 * -EINTR if @intr was set to true and a signal is pending.
 50 */
 51int ttm_backup_copy_page(struct file *backup, struct page *dst,
 52			 pgoff_t handle, bool intr)
 53{
 54	struct address_space *mapping = backup->f_mapping;
 55	struct folio *from_folio;
 56	pgoff_t idx = ttm_backup_handle_to_shmem_idx(handle);
 57
 58	from_folio = shmem_read_folio(mapping, idx);
 59	if (IS_ERR(from_folio))
 60		return PTR_ERR(from_folio);
 61
 62	copy_highpage(dst, folio_file_page(from_folio, idx));
 63	folio_put(from_folio);
 64
 65	return 0;
 66}
 67
 68/**
 69 * ttm_backup_backup_page() - Backup a page
 70 * @backup: The struct backup pointer to use.
 71 * @page: The page to back up.
 72 * @writeback: Whether to perform immediate writeback of the page.
 73 * This may have performance implications.
 74 * @idx: A unique integer for each page and each struct backup.
 75 * This allows the backup implementation to avoid managing
 76 * its address space separately.
 77 * @page_gfp: The gfp value used when the page was allocated.
 78 * This is used for accounting purposes.
 79 * @alloc_gfp: The gfp to be used when allocating memory.
 80 *
 81 * Context: If called from reclaim context, the caller needs to
 82 * assert that the shrinker gfp has __GFP_FS set, to avoid
 83 * deadlocking on lock_page(). If @writeback is set to true and
 84 * called from reclaim context, the caller also needs to assert
 85 * that the shrinker gfp has __GFP_IO set, since without it,
 86 * we're not allowed to start backup IO.
 87 *
 88 * Return: A handle on success. Negative error code on failure.
 89 *
 90 * Note: This function could be extended to back up a folio and
 91 * implementations would then split the folio internally if needed.
 92 * Drawback is that the caller would then have to keep track of
 93 * the folio size- and usage.
 94 */
 95s64
 96ttm_backup_backup_page(struct file *backup, struct page *page,
 97		       bool writeback, pgoff_t idx, gfp_t page_gfp,
 98		       gfp_t alloc_gfp)
 99{
100	struct address_space *mapping = backup->f_mapping;
101	unsigned long handle = 0;
102	struct folio *to_folio;
103	int ret;
104
105	to_folio = shmem_read_folio_gfp(mapping, idx, alloc_gfp);
106	if (IS_ERR(to_folio))
107		return PTR_ERR(to_folio);
108
109	folio_mark_accessed(to_folio);
110	folio_lock(to_folio);
111	folio_mark_dirty(to_folio);
112	copy_highpage(folio_file_page(to_folio, idx), page);
113	handle = ttm_backup_shmem_idx_to_handle(idx);
114
115	if (writeback && !folio_mapped(to_folio) &&
116	    folio_clear_dirty_for_io(to_folio)) {
117		folio_set_reclaim(to_folio);
118		ret = shmem_writeout(to_folio, NULL, NULL);
119		if (!folio_test_writeback(to_folio))
120			folio_clear_reclaim(to_folio);
121		/*
122		 * If writeout succeeds, it unlocks the folio.	errors
123		 * are otherwise dropped, since writeout is only best
124		 * effort here.
125		 */
126		if (ret)
127			folio_unlock(to_folio);
128	} else {
129		folio_unlock(to_folio);
130	}
131
132	folio_put(to_folio);
133
134	return handle;
135}
136
137/**
138 * ttm_backup_fini() - Free the struct backup resources after last use.
139 * @backup: Pointer to the struct backup whose resources to free.
140 *
141 * After a call to this function, it's illegal to use the @backup pointer.
142 */
143void ttm_backup_fini(struct file *backup)
144{
145	fput(backup);
146}
147
148/**
149 * ttm_backup_bytes_avail() - Report the approximate number of bytes of backup space
150 * left for backup.
151 *
152 * This function is intended also for driver use to indicate whether a
153 * backup attempt is meaningful.
154 *
155 * Return: An approximate size of backup space available.
156 */
157u64 ttm_backup_bytes_avail(void)
158{
159	/*
160	 * The idea behind backing up to shmem is that shmem objects may
161	 * eventually be swapped out. So no point swapping out if there
162	 * is no or low swap-space available. But the accuracy of this
163	 * number also depends on shmem actually swapping out backed-up
164	 * shmem objects without too much buffering.
165	 */
166	return (u64)get_nr_swap_pages() << PAGE_SHIFT;
167}
168EXPORT_SYMBOL_GPL(ttm_backup_bytes_avail);
169
170/**
171 * ttm_backup_shmem_create() - Create a shmem-based struct backup.
172 * @size: The maximum size (in bytes) to back up.
173 *
174 * Create a backup utilizing shmem objects.
175 *
176 * Return: A pointer to a struct file on success,
177 * an error pointer on error.
178 */
179struct file *ttm_backup_shmem_create(loff_t size)
180{
181	return shmem_file_setup("ttm shmem backup", size, 0);
182}