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Message-ID: <20230727162343.1415598-4-hannes@cmpxchg.org>
Date: Thu, 27 Jul 2023 12:22:25 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Yosry Ahmed <yosryahmed@...gle.com>, Nhat Pham <nphamcs@...il.com>,
Domenico Cerasuolo <cerasuolodomenico@...il.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] mm: zswap: kill zswap_get_swap_cache_page()
The __read_swap_cache_async() interface isn't more difficult to
understand than what the helper abstracts. Save the indirection and a
level of indentation for the primary work of the writeback func.
Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
mm/zswap.c | 142 ++++++++++++++++++++---------------------------------
1 file changed, 53 insertions(+), 89 deletions(-)
diff --git a/mm/zswap.c b/mm/zswap.c
index e34ac89e6098..bba4ead672be 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1016,43 +1016,6 @@ static int zswap_enabled_param_set(const char *val,
/*********************************
* writeback code
**********************************/
-/* return enum for zswap_get_swap_cache_page */
-enum zswap_get_swap_ret {
- ZSWAP_SWAPCACHE_NEW,
- ZSWAP_SWAPCACHE_EXIST,
- ZSWAP_SWAPCACHE_FAIL,
-};
-
-/*
- * zswap_get_swap_cache_page
- *
- * This is an adaption of read_swap_cache_async()
- *
- * This function tries to find a page with the given swap entry
- * in the swapper_space address space (the swap cache). If the page
- * is found, it is returned in retpage. Otherwise, a page is allocated,
- * added to the swap cache, and returned in retpage.
- *
- * If success, the swap cache page is returned in retpage
- * Returns ZSWAP_SWAPCACHE_EXIST if page was already in the swap cache
- * Returns ZSWAP_SWAPCACHE_NEW if the new page needs to be populated,
- * the new page is added to swapcache and locked
- * Returns ZSWAP_SWAPCACHE_FAIL on error
- */
-static int zswap_get_swap_cache_page(swp_entry_t entry,
- struct page **retpage)
-{
- bool page_was_allocated;
-
- *retpage = __read_swap_cache_async(entry, GFP_KERNEL,
- NULL, 0, &page_was_allocated);
- if (page_was_allocated)
- return ZSWAP_SWAPCACHE_NEW;
- if (!*retpage)
- return ZSWAP_SWAPCACHE_FAIL;
- return ZSWAP_SWAPCACHE_EXIST;
-}
-
/*
* Attempts to free an entry by adding a page to the swap cache,
* decompressing the entry data into the page, and issuing a
@@ -1073,7 +1036,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
struct scatterlist input, output;
struct crypto_acomp_ctx *acomp_ctx;
struct zpool *pool = entry->pool->zpool;
-
+ bool page_was_allocated;
u8 *src, *tmp = NULL;
unsigned int dlen;
int ret;
@@ -1088,65 +1051,66 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
}
/* try to allocate swap cache page */
- switch (zswap_get_swap_cache_page(swpentry, &page)) {
- case ZSWAP_SWAPCACHE_FAIL: /* no memory or invalidate happened */
+ page = __read_swap_cache_async(swpentry, GFP_KERNEL, NULL, 0,
+ &page_was_allocated);
+ if (!page) {
ret = -ENOMEM;
goto fail;
+ }
- case ZSWAP_SWAPCACHE_EXIST:
- /* page is already in the swap cache, ignore for now */
+ /* Found an existing page, we raced with load/swapin */
+ if (!page_was_allocated) {
put_page(page);
ret = -EEXIST;
goto fail;
+ }
- case ZSWAP_SWAPCACHE_NEW: /* page is locked */
- /*
- * Having a local reference to the zswap entry doesn't exclude
- * swapping from invalidating and recycling the swap slot. Once
- * the swapcache is secured against concurrent swapping to and
- * from the slot, recheck that the entry is still current before
- * writing.
- */
- spin_lock(&tree->lock);
- if (zswap_rb_search(&tree->rbroot, swp_offset(entry->swpentry)) != entry) {
- spin_unlock(&tree->lock);
- delete_from_swap_cache(page_folio(page));
- ret = -ENOMEM;
- goto fail;
- }
+ /*
+ * Page is locked, and the swapcache is now secured against
+ * concurrent swapping to and from the slot. Verify that the
+ * swap entry hasn't been invalidated and recycled behind our
+ * backs (our zswap_entry reference doesn't prevent that), to
+ * avoid overwriting a new swap page with old compressed data.
+ */
+ spin_lock(&tree->lock);
+ if (zswap_rb_search(&tree->rbroot, swp_offset(entry->swpentry)) != entry) {
spin_unlock(&tree->lock);
+ delete_from_swap_cache(page_folio(page));
+ ret = -ENOMEM;
+ goto fail;
+ }
+ spin_unlock(&tree->lock);
- /* decompress */
- acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
- dlen = PAGE_SIZE;
+ /* decompress */
+ acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
+ dlen = PAGE_SIZE;
- src = zpool_map_handle(pool, entry->handle, ZPOOL_MM_RO);
- if (!zpool_can_sleep_mapped(pool)) {
- memcpy(tmp, src, entry->length);
- src = tmp;
- zpool_unmap_handle(pool, entry->handle);
- }
+ src = zpool_map_handle(pool, entry->handle, ZPOOL_MM_RO);
+ if (!zpool_can_sleep_mapped(pool)) {
+ memcpy(tmp, src, entry->length);
+ src = tmp;
+ zpool_unmap_handle(pool, entry->handle);
+ }
- mutex_lock(acomp_ctx->mutex);
- sg_init_one(&input, src, entry->length);
- sg_init_table(&output, 1);
- sg_set_page(&output, page, PAGE_SIZE, 0);
- acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);
- ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
- dlen = acomp_ctx->req->dlen;
- mutex_unlock(acomp_ctx->mutex);
-
- if (!zpool_can_sleep_mapped(pool))
- kfree(tmp);
- else
- zpool_unmap_handle(pool, entry->handle);
+ mutex_lock(acomp_ctx->mutex);
+ sg_init_one(&input, src, entry->length);
+ sg_init_table(&output, 1);
+ sg_set_page(&output, page, PAGE_SIZE, 0);
+ acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);
+ ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
+ dlen = acomp_ctx->req->dlen;
+ mutex_unlock(acomp_ctx->mutex);
+
+ if (!zpool_can_sleep_mapped(pool))
+ kfree(tmp);
+ else
+ zpool_unmap_handle(pool, entry->handle);
- BUG_ON(ret);
- BUG_ON(dlen != PAGE_SIZE);
+ BUG_ON(ret);
+ BUG_ON(dlen != PAGE_SIZE);
- /* page is up to date */
- SetPageUptodate(page);
- }
+ /* page is up to date */
+ SetPageUptodate(page);
/* move it to the tail of the inactive list after end_writeback */
SetPageReclaim(page);
@@ -1157,16 +1121,16 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
zswap_written_back_pages++;
return ret;
+
fail:
if (!zpool_can_sleep_mapped(pool))
kfree(tmp);
/*
- * if we get here due to ZSWAP_SWAPCACHE_EXIST
- * a load may be happening concurrently.
- * it is safe and okay to not free the entry.
- * it is also okay to return !0
- */
+ * If we get here because the page is already in swapcache, a
+ * load may be happening concurrently. It is safe and okay to
+ * not free the entry. It is also okay to return !0.
+ */
return ret;
}
--
2.41.0
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