Re: [RFC PATCH 7/7] mm: zswap: Use acomp virtual address interface

[Herbert Xu <herbert@gondor.apana.org.au>]

On Fri, Feb 28, 2025 at 04:13:08PM +0800, Herbert Xu wrote:
>
> I'll respin this.

FWIW this is what the interface looks like.  Does it look OK?
Longer term hardware offload drivers should handle these non-DMA
pointers directly by having their own buffers.  For the time being
I'm simply redirecting these to a software fallback.

diff --git a/mm/zswap.c b/mm/zswap.c
index 2b5a2398a9be..2fd241c65f80 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -994,30 +994,16 @@ static void zswap_decompress(struct zswap_entry *entry, struct folio *folio)
 
 	acomp_ctx = acomp_ctx_get_cpu_lock(entry->pool);
 	src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
-	/*
-	 * If zpool_map_handle is atomic, we cannot reliably utilize its mapped buffer
-	 * to do crypto_acomp_decompress() which might sleep. In such cases, we must
-	 * resort to copying the buffer to a temporary one.
-	 * Meanwhile, zpool_map_handle() might return a non-linearly mapped buffer,
-	 * such as a kmap address of high memory or even ever a vmap address.
-	 * However, sg_init_one is only equipped to handle linearly mapped low memory.
-	 * In such cases, we also must copy the buffer to a temporary and lowmem one.
-	 */
-	if ((acomp_ctx->is_sleepable && !zpool_can_sleep_mapped(zpool)) ||
-	    !virt_addr_valid(src)) {
-		memcpy(acomp_ctx->buffer, src, entry->length);
-		src = acomp_ctx->buffer;
-		zpool_unmap_handle(zpool, entry->handle);
-	}
-
 	dst = kmap_local_folio(folio, 0);
-	acomp_request_set_virt(acomp_ctx->req, src, dst, entry->length, PAGE_SIZE);
+	if (!zpool_can_sleep_mapped(zpool) || !virt_addr_valid(src))
+		acomp_request_set_nondma(acomp_ctx->req, src, dst, entry->length, PAGE_SIZE);
+	else
+		acomp_request_set_virt(acomp_ctx->req, src, dst, entry->length, PAGE_SIZE);
 	BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait));
 	kunmap_local(dst);
 	BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
 
-	if (src != acomp_ctx->buffer)
-		zpool_unmap_handle(zpool, entry->handle);
+	zpool_unmap_handle(zpool, entry->handle);
 	acomp_ctx_put_unlock(acomp_ctx);
 }

-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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