[PATCH RFC 4/4] fs/pipe: remove the old on-stack prealloc helpers and tmp_page[2]

[Breno Leitao]

With the write path converted to the per-pipe pool, the old on-stack
prealloc helpers (anon_pipe_get_page_prealloc, anon_pipe_refill_tmp_pages,
anon_pipe_free_pages) and the tmp_page[2] cache have no remaining users.
Remove them.

Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
---
 fs/pipe.c                 | 66 -----------------------------------------------
 include/linux/pipe_fs_i.h |  2 --
 2 files changed, 68 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 070fba8c865c1..108e498aee47e 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -111,40 +111,6 @@ void pipe_double_lock(struct pipe_inode_info *pipe1,
 	pipe_lock(pipe2);
 }
 
-/*
- * Pre-allocate pages outside pipe->mutex for multi-page writes.
- * alloc_page() with GFP_HIGHUSER can sleep in reclaim and runs memcg
- * charging; doing it under the mutex stalls a concurrent reader.
- *
- * Loop alloc_page() instead of alloc_pages_bulk_*(): the bulk path refuses
- * __GFP_ACCOUNT under memcg (see commit 8dcb3060d81d "memcg: page_alloc:
- * skip bulk allocator for __GFP_ACCOUNT") and silently degrades to a single
- * page. A per-page loop keeps memcg accounting and the task NUMA mempolicy
- * honoured for every page; the per-call overhead is small compared to the
- * pipe->mutex hold-time being shrunk. Any shortfall is covered by the
- * in-lock alloc_page() fallback in anon_pipe_get_page().
- */
-static void __maybe_unused anon_pipe_get_page_prealloc(struct anon_pipe_prealloc *prealloc,
-						       size_t total_len)
-{
-	unsigned int want, i;
-	struct page *page;
-
-	prealloc->count = 0;
-	if (total_len <= PAGE_SIZE)
-		return;
-
-	want = min_t(unsigned int, DIV_ROUND_UP(total_len, PAGE_SIZE),
-		     PIPE_PREALLOC_MAX);
-
-	for (i = 0; i < want; i++) {
-		page = alloc_page(GFP_HIGHUSER | __GFP_ACCOUNT);
-		if (!page)
-			break;
-		prealloc->pages[prealloc->count++] = page;
-	}
-}
-
 static struct page *anon_pipe_prealloc_pop(struct anon_pipe_prealloc *prealloc)
 {
 	if (!prealloc->count)
@@ -242,38 +208,6 @@ static void anon_pipe_put_page(struct pipe_inode_info *pipe,
 	put_page(page);
 }
 
-/*
- * Stash leftover prealloc pages in tmp_page[] so the next write to this
- * pipe gets a hot page without entering the allocator.
- */
-static void __maybe_unused anon_pipe_refill_tmp_pages(struct pipe_inode_info *pipe,
-						      struct anon_pipe_prealloc *prealloc)
-{
-	int i, idx;
-
-	if (!prealloc->count)
-		return;
-
-	for (i = 0; i < ARRAY_SIZE(pipe->tmp_page); i++) {
-		if (pipe->tmp_page[i])
-			continue;
-		if (!prealloc->count)
-			return;
-		idx = --prealloc->count;
-		pipe->tmp_page[i] = prealloc->pages[idx];
-		prealloc->pages[idx] = NULL;
-	}
-}
-
-/* Runs after mutex_unlock() to keep put_page() out of the critical section. */
-static void __maybe_unused anon_pipe_free_pages(struct anon_pipe_prealloc *prealloc)
-{
-	while (prealloc->count) {
-		prealloc->count--;
-		put_page(prealloc->pages[prealloc->count]);
-	}
-}
-
 static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
 				  struct pipe_buffer *buf)
 {
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 796860cbddf30..6bd0d956691cb 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -84,7 +84,6 @@ struct anon_pipe_prealloc {
  *	@max_usage: The maximum number of slots that may be used in the ring
  *	@ring_size: total number of buffers (should be a power of 2)
  *	@nr_accounted: The amount this pipe accounts for in user->pipe_bufs
- *	@tmp_page: cached released page
  *	@prealloc: per-pipe page preallocation pool
  *	@readers: number of current readers of this pipe
  *	@writers: number of current writers of this pipe
@@ -116,7 +115,6 @@ struct pipe_inode_info {
 #ifdef CONFIG_WATCH_QUEUE
 	bool note_loss;
 #endif
-	struct page *tmp_page[2];
 	struct anon_pipe_prealloc prealloc;
 	struct fasync_struct *fasync_readers;
 	struct fasync_struct *fasync_writers;

-- 
2.53.0-Meta