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Date: Mon, 24 Jan 2022 00:52:46 -0800 From: Christoph Hellwig <hch@...radead.org> To: NeilBrown <neilb@...e.de> Cc: Trond Myklebust <trond.myklebust@...merspace.com>, Anna Schumaker <anna.schumaker@...app.com>, Chuck Lever <chuck.lever@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, Mel Gorman <mgorman@...e.de>, Christoph Hellwig <hch@...radead.org>, David Howells <dhowells@...hat.com>, linux-nfs@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 09/23] MM: submit multipage reads for SWP_FS_OPS swap-space On Mon, Jan 24, 2022 at 02:48:32PM +1100, NeilBrown wrote: > swap_readpage() is given one page at a time, but maybe called repeatedly > in succession. > For block-device swapspace, the blk_plug functionality allows the > multiple pages to be combined together at lower layers. > That cannot be used for SWP_FS_OPS as blk_plug may not exist - it is > only active when CONFIG_BLOCK=y. Consequently all swap reads over NFS > are single page reads. > > With this patch we pass in a pointer-to-pointer when swap_readpage can > store state between calls - much like the effect of blk_plug. After > calling swap_readpage() some number of times, the state will be passed > to swap_read_unplug() which can submit the combined request. > > Some caller currently call blk_finish_plug() *before* the final call to > swap_readpage(), so the last page cannot be included. This patch moves > blk_finish_plug() to after the last call, and calls swap_read_unplug() > there too. Buildbot complais that we might need a forward declaration of struct swap_iocb, but otherwise this looks good: Reviewed-by: Christoph Hellwig <hch@....de>
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