}
/*
- * The LRU management algorithm is dopey-but-simple. Sorry.
+ * Install a buffer_head into this cpu's LRU. If not already in the LRU, it is
+ * inserted at the front, and the buffer_head at the back if any is evicted.
+ * Or, if already in the LRU it is moved to the front.
*/
static void bh_lru_install(struct buffer_head *bh)
{
- struct buffer_head *evictee = NULL;
+ struct buffer_head *evictee = bh;
+ struct bh_lru *b;
+ int i;
check_irqs_on();
bh_lru_lock();
- if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
- struct buffer_head *bhs[BH_LRU_SIZE];
- int in;
- int out = 0;
-
- get_bh(bh);
- bhs[out++] = bh;
- for (in = 0; in < BH_LRU_SIZE; in++) {
- struct buffer_head *bh2 =
- __this_cpu_read(bh_lrus.bhs[in]);
- if (bh2 == bh) {
- __brelse(bh2);
- } else {
- if (out >= BH_LRU_SIZE) {
- BUG_ON(evictee != NULL);
- evictee = bh2;
- } else {
- bhs[out++] = bh2;
- }
- }
+ b = this_cpu_ptr(&bh_lrus);
+ for (i = 0; i < BH_LRU_SIZE; i++) {
+ swap(evictee, b->bhs[i]);
+ if (evictee == bh) {
+ bh_lru_unlock();
+ return;
}
- while (out < BH_LRU_SIZE)
- bhs[out++] = NULL;
- memcpy(this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
}
- bh_lru_unlock();
- if (evictee)
- __brelse(evictee);
+ get_bh(bh);
+ bh_lru_unlock();
+ brelse(evictee);
}
/*
}
EXPORT_SYMBOL(bh_submit_read);
+/*
+ * Seek for SEEK_DATA / SEEK_HOLE within @page, starting at @lastoff.
+ *
+ * Returns the offset within the file on success, and -ENOENT otherwise.
+ */
+static loff_t
+page_seek_hole_data(struct page *page, loff_t lastoff, int whence)
+{
+ loff_t offset = page_offset(page);
+ struct buffer_head *bh, *head;
+ bool seek_data = whence == SEEK_DATA;
+
+ if (lastoff < offset)
+ lastoff = offset;
+
+ bh = head = page_buffers(page);
+ do {
+ offset += bh->b_size;
+ if (lastoff >= offset)
+ continue;
+
+ /*
+ * Unwritten extents that have data in the page cache covering
+ * them can be identified by the BH_Unwritten state flag.
+ * Pages with multiple buffers might have a mix of holes, data
+ * and unwritten extents - any buffer with valid data in it
+ * should have BH_Uptodate flag set on it.
+ */
+
+ if ((buffer_unwritten(bh) || buffer_uptodate(bh)) == seek_data)
+ return lastoff;
+
+ lastoff = offset;
+ } while ((bh = bh->b_this_page) != head);
+ return -ENOENT;
+}
+
+/*
+ * Seek for SEEK_DATA / SEEK_HOLE in the page cache.
+ *
+ * Within unwritten extents, the page cache determines which parts are holes
+ * and which are data: unwritten and uptodate buffer heads count as data;
+ * everything else counts as a hole.
+ *
+ * Returns the resulting offset on successs, and -ENOENT otherwise.
+ */
+loff_t
+page_cache_seek_hole_data(struct inode *inode, loff_t offset, loff_t length,
+ int whence)
+{
+ pgoff_t index = offset >> PAGE_SHIFT;
+ pgoff_t end = DIV_ROUND_UP(offset + length, PAGE_SIZE);
+ loff_t lastoff = offset;
+ struct pagevec pvec;
+
+ if (length <= 0)
+ return -ENOENT;
+
+ pagevec_init(&pvec, 0);
+
+ do {
+ unsigned want, nr_pages, i;
+
+ want = min_t(unsigned, end - index, PAGEVEC_SIZE);
+ nr_pages = pagevec_lookup(&pvec, inode->i_mapping, index, want);
+ if (nr_pages == 0)
+ break;
+
+ for (i = 0; i < nr_pages; i++) {
+ struct page *page = pvec.pages[i];
+
+ /*
+ * At this point, the page may be truncated or
+ * invalidated (changing page->mapping to NULL), or
+ * even swizzled back from swapper_space to tmpfs file
+ * mapping. However, page->index will not change
+ * because we have a reference on the page.
+ *
+ * If current page offset is beyond where we've ended,
+ * we've found a hole.
+ */
+ if (whence == SEEK_HOLE &&
+ lastoff < page_offset(page))
+ goto check_range;
+
+ /* Searching done if the page index is out of range. */
+ if (page->index >= end)
+ goto not_found;
+
+ lock_page(page);
+ if (likely(page->mapping == inode->i_mapping) &&
+ page_has_buffers(page)) {
+ lastoff = page_seek_hole_data(page, lastoff, whence);
+ if (lastoff >= 0) {
+ unlock_page(page);
+ goto check_range;
+ }
+ }
+ unlock_page(page);
+ lastoff = page_offset(page) + PAGE_SIZE;
+ }
+
+ /* Searching done if fewer pages returned than wanted. */
+ if (nr_pages < want)
+ break;
+
+ index = pvec.pages[i - 1]->index + 1;
+ pagevec_release(&pvec);
+ } while (index < end);
+
+ /* When no page at lastoff and we are not done, we found a hole. */
+ if (whence != SEEK_HOLE)
+ goto not_found;
+
+check_range:
+ if (lastoff < offset + length)
+ goto out;
+not_found:
+ lastoff = -ENOENT;
+out:
+ pagevec_release(&pvec);
+ return lastoff;
+}
+
void __init buffer_init(void)
{
unsigned long nrpages;
projects / karo-tx-linux.git / blobdiff