linux-kernel - Re: [PATCH 3/6] shmem: account for large order folios

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Message-ID: <ZQRf2pGWurrE0uO+@casper.infradead.org>
Date:   Fri, 15 Sep 2023 14:44:58 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Daniel Gomez <da.gomez@...sung.com>
Cc:     "minchan@...nel.org" <minchan@...nel.org>,
        "senozhatsky@...omium.org" <senozhatsky@...omium.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "djwong@...nel.org" <djwong@...nel.org>,
        "hughd@...gle.com" <hughd@...gle.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mcgrof@...nel.org" <mcgrof@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "gost.dev@...sung.com" <gost.dev@...sung.com>,
        Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH 3/6] shmem: account for large order folios

On Fri, Sep 15, 2023 at 09:51:26AM +0000, Daniel Gomez wrote:
> +	xas_for_each(&xas, folio, max) {
> +		if (xas_retry(&xas, folio))
>  			continue;
> -		if (xa_is_value(page))
> -			swapped++;
> +		if (xa_is_value(folio))
> +			swapped += (folio_nr_pages(folio));

Unnecessary parens.

> @@ -1006,10 +1006,12 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
>  			folio = fbatch.folios[i];
>  
>  			if (xa_is_value(folio)) {
> +				long swaps_freed;
>  				if (unfalloc)
>  					continue;
> -				nr_swaps_freed += !shmem_free_swap(mapping,
> -							indices[i], folio);
> +				swaps_freed = folio_nr_pages(folio);
> +				if (!shmem_free_swap(mapping, indices[i], folio))
> +					nr_swaps_freed += swaps_freed;

Broader change (indeed, in a separate patch), why not make
shmem_free_swap() return the number of pages freed, rather than
returning an errno?

> @@ -1075,14 +1077,16 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
>  			folio = fbatch.folios[i];
>  
>  			if (xa_is_value(folio)) {
> +				long swaps_freed;
>  				if (unfalloc)
>  					continue;
> +				swaps_freed = folio_nr_pages(folio);
>  				if (shmem_free_swap(mapping, indices[i], folio)) {
>  					/* Swap was replaced by page: retry */
>  					index = indices[i];
>  					break;
>  				}
> -				nr_swaps_freed++;
> +				nr_swaps_freed += swaps_freed;
>  				continue;

... seems like both callers would prefer that.