linux-kernel - Re: [PATCH v2 5/6] mm: zswap: store incompressible page as-is

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Message-ID: <CAPpoddfySkGpD5hKgqUAAMgMp2vWcivg1AzcyYh_NP1-ZsGkug@mail.gmail.com>
Date: Mon, 8 Jul 2024 22:44:47 +0900
From: Takero Funaki <flintglass@...il.com>
To: Chengming Zhou <chengming.zhou@...ux.dev>
Cc: Johannes Weiner <hannes@...xchg.org>, Yosry Ahmed <yosryahmed@...gle.com>, 
	Nhat Pham <nphamcs@...il.com>, Jonathan Corbet <corbet@....net>, 
	Andrew Morton <akpm@...ux-foundation.org>, 
	Domenico Cerasuolo <cerasuolodomenico@...il.com>, linux-mm@...ck.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/6] mm: zswap: store incompressible page as-is

2024年7月8日(月) 12:56 Chengming Zhou <chengming.zhou@...ux.dev>:

> >       comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
> >       dlen = acomp_ctx->req->dlen;
> > -     if (comp_ret)
> > +
> > +     /* coa_compress returns -EINVAL for errors including insufficient dlen */
> > +     if (comp_ret && comp_ret != -EINVAL)
> >               goto unlock;
>
> Seems we don't need to care about? "comp_ret" is useless anymore.
>
> Just:
>
> if (comp_ret || dlen > PAGE_SIZE - 64)
>         dlen = PAGE_SIZE;
>
> And remove the checkings of comp_ret at the end.
>

>
> We actually don't need to hold mutex if we are just copying folio.
>
> Thanks.
>

Thanks for reviewing.

For comp_ret, can we consolidate all possible error codes as
incompressible data?
if we do not need to distinguish -EINVAL and the others, diff v2..v3
can be like:

@@ -62,8 +62,6 @@ static u64 zswap_pool_limit_hit;
 static u64 zswap_written_back_pages;
 /* Store failed due to a reclaim failure after pool limit was reached */
 static u64 zswap_reject_reclaim_fail;
-/* Store failed due to compression algorithm failure */
-static u64 zswap_reject_compress_fail;
 /* Compressed page was too big for the allocator to (optimally) store */
 static u64 zswap_reject_compress_poor;
 /* Store failed because underlying allocator could not get memory */
@@ -1043,10 +1041,6 @@ static bool zswap_compress(struct folio *folio,
struct zswap_entry *entry)
        comp_ret =
crypto_wait_req(crypto_acomp_compress(acomp_ctx->req),
&acomp_ctx->wait);
        dlen = acomp_ctx->req->dlen;

-       /* coa_compress returns -EINVAL for errors including
insufficient dlen */
-       if (comp_ret && comp_ret != -EINVAL)
-               goto unlock;
-
        /*
         * If the data cannot be compressed well, store the data as-is.
         * Switching by a threshold at
@@ -1056,7 +1050,8 @@ static bool zswap_compress(struct folio *folio,
struct zswap_entry *entry)
         */
        if (comp_ret || dlen > PAGE_SIZE - 64) {
                /* we do not use compressed result anymore */
-               comp_ret = 0;
+               mutex_unlock(&acomp_ctx->mutex);
+               acomp_ctx = NULL;
                dlen = PAGE_SIZE;
        }
        zpool = zswap_find_zpool(entry);
@@ -1083,12 +1078,11 @@ static bool zswap_compress(struct folio
*folio, struct zswap_entry *entry)
 unlock:
        if (alloc_ret == -ENOSPC)
                zswap_reject_compress_poor++;
-       else if (comp_ret)
-               zswap_reject_compress_fail++;
        else if (alloc_ret)
                zswap_reject_alloc_fail++;

-       mutex_unlock(&acomp_ctx->mutex);
+       if (acomp_ctx)
+               mutex_unlock(&acomp_ctx->mutex);
        return comp_ret == 0 && alloc_ret == 0;
 }

@@ -1886,8 +1880,6 @@ static int zswap_debugfs_init(void)
                           zswap_debugfs_root, &zswap_reject_alloc_fail);
        debugfs_create_u64("reject_kmemcache_fail", 0444,
                           zswap_debugfs_root, &zswap_reject_kmemcache_fail);
-       debugfs_create_u64("reject_compress_fail", 0444,
-                          zswap_debugfs_root, &zswap_reject_compress_fail);
        debugfs_create_u64("reject_compress_poor", 0444,
                           zswap_debugfs_root, &zswap_reject_compress_poor);
        debugfs_create_u64("written_back_pages", 0444,