From 9ead7efc6f3f2b46c4ec68209bca4888cfbd4c19 Mon Sep 17 00:00:00 2001
From: Keith Busch <kbusch@kernel.org>
Date: Mon, 29 Apr 2024 03:23:08 -0700
Subject: [PATCH] brd: implement discard support
The ramdisk memory utilization can only go up when data is written to
new pages. Implement discard to provide the possibility to reduce memory
usage for pages no longer in use. Aligned discards will free the
associated pages, if any, and determinisitically return zeroed data
until written again.
Signed-off-by: Keith Busch <kbusch@kernel.org>
Link: https://lore.kernel.org/r/20240429102308.147627-1-kbusch@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
drivers/block/brd.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index b900fe9e00308..558d8e6705660 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -222,6 +222,23 @@ out:
return err;
}
+static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size)
+{
+ sector_t aligned_sector = (sector + PAGE_SECTORS) & ~PAGE_SECTORS;
+ struct page *page;
+
+ size -= (aligned_sector - sector) * SECTOR_SIZE;
+ xa_lock(&brd->brd_pages);
+ while (size >= PAGE_SIZE && aligned_sector < rd_size * 2) {
+ page = __xa_erase(&brd->brd_pages, aligned_sector >> PAGE_SECTORS_SHIFT);
+ if (page)
+ __free_page(page);
+ aligned_sector += PAGE_SECTORS;
+ size -= PAGE_SIZE;
+ }
+ xa_unlock(&brd->brd_pages);
+}
+
static void brd_submit_bio(struct bio *bio)
{
struct brd_device *brd = bio->bi_bdev->bd_disk->private_data;
@@ -229,6 +246,12 @@ static void brd_submit_bio(struct bio *bio)
struct bio_vec bvec;
struct bvec_iter iter;
+ if (unlikely(op_is_discard(bio->bi_opf))) {
+ brd_do_discard(brd, sector, bio->bi_iter.bi_size);
+ bio_endio(bio);
+ return;
+ }
+
bio_for_each_segment(bvec, bio, iter) {
unsigned int len = bvec.bv_len;
int err;
@@ -309,6 +332,9 @@ static int brd_alloc(int i)
* is harmless)
*/
.physical_block_size = PAGE_SIZE,
+ .max_hw_discard_sectors = UINT_MAX,
+ .max_discard_segments = 1,
+ .discard_granularity = PAGE_SIZE,
};
list_for_each_entry(brd, &brd_devices, brd_list)
--
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