linux-kernel - [RFC 1/3] mm/vmalloc: alloc GFP

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Date:   Mon, 18 Oct 2021 13:47:10 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     <linux-mm@...ck.org>
Cc:     Dave Chinner <david@...morbit.com>, Neil Brown <neilb@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Uladzislau Rezki <urezki@...il.com>,
        <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Jeff Layton <jlayton@...nel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: [RFC 1/3] mm/vmalloc: alloc GFP_NO{FS,IO} for vmalloc

From: Michal Hocko <mhocko@...e.com>

vmalloc historically hasn't supported GFP_NO{FS,IO} requests because
page table allocations do not support externally provided gfp mask
and performed GFP_KERNEL like allocations.

Since few years we have scope (memalloc_no{fs,io}_{save,restore}) APIs
to enforce NOFS and NOIO constrains implicitly to all allocators within
the scope. There was a hope that those scopes would be defined on a
higher level when the reclaim recursion boundary starts/stops (e.g. when
a lock required during the memory reclaim is required etc.). It seems
that not all NOFS/NOIO users have adopted this approach and instead
they have taken a workaround approach to wrap a single [k]vmalloc
allocation by a scope API.

These workarounds do not serve the purpose of a better reclaim recursion
documentation and reduction of explicit GFP_NO{FS,IO} usege so let's
just provide them with the semantic they are asking for without a need
for workarounds.

Add support for GFP_NOFS and GFP_NOIO to vmalloc directly. All internal
allocations already comply with the given gfp_mask. The only current
exception is vmap_pages_range which maps kernel page tables. Infer the
proper scope API based on the given gfp mask.

Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 mm/vmalloc.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d77830ff604c..7455c89598d3 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2889,6 +2889,8 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 	unsigned long array_size;
 	unsigned int nr_small_pages = size >> PAGE_SHIFT;
 	unsigned int page_order;
+	unsigned int flags;
+	int ret;

 	array_size = (unsigned long)nr_small_pages * sizeof(struct page *);
 	gfp_mask |= __GFP_NOWARN;
@@ -2930,8 +2932,24 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 		goto fail;
 	}

-	if (vmap_pages_range(addr, addr + size, prot, area->pages,
-			page_shift) < 0) {
+	/*
+	 * page tables allocations ignore external gfp mask, enforce it
+	 * by the scope API
+	 */
+	if ((gfp_mask & (__GFP_FS | __GFP_IO)) == __GFP_IO)
+		flags = memalloc_nofs_save();
+	else if (!(gfp_mask & (__GFP_FS | __GFP_IO)))
+		flags = memalloc_noio_save();
+
+	ret = vmap_pages_range(addr, addr + size, prot, area->pages,
+			page_shift);
+
+	if ((gfp_mask & (__GFP_FS | __GFP_IO)) == __GFP_IO)
+		memalloc_nofs_restore(flags);
+	else if (!(gfp_mask & (__GFP_FS | __GFP_IO)))
+		memalloc_noio_restore(flags);
+
+	if (ret < 0) {
 		warn_alloc(gfp_mask, NULL,
 			"vmalloc error: size %lu, failed to map pages",
 			area->nr_pages * PAGE_SIZE);
-- 
2.30.2