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Date: Mon, 6 Apr 2020 10:20:33 -0700 From: Roman Gushchin <guro@...com> To: Theodore Ts'o <tytso@....edu> CC: Linux FS Devel <linux-fsdevel@...r.kernel.org>, linux-ext4 <linux-ext4@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Alexander Viro <viro@...iv.linux.org.uk>, Andrew Perepechko <andrew.perepechko@...gate.com>, <adilger@...ger.ca>, Gioh Kim <gioh.kim@....com>, Jan Kara <jack@...e.cz> Subject: Re: [PATCH v2] ext4: use non-movable memory for superblock readahead On Sat, Feb 29, 2020 at 12:49:13AM -0700, Andreas Dilger wrote: > On Feb 28, 2020, at 5:14 PM, Roman Gushchin <guro@...com> wrote: > > > > Since commit a8ac900b8163 ("ext4: use non-movable memory for the > > superblock") buffers for ext4 superblock were allocated using > > the sb_bread_unmovable() helper which allocated buffer heads > > out of non-movable memory blocks. It was necessarily to not block > > page migrations and do not cause cma allocation failures. > > > > However commit 85c8f176a611 ("ext4: preload block group descriptors") > > broke this by introducing pre-reading of the ext4 superblock. > > The problem is that __breadahead() is using __getblk() underneath, > > which allocates buffer heads out of movable memory. > > > > It resulted in page migration failures I've seen on a machine > > with an ext4 partition and a preallocated cma area. > > > > Fix this by introducing sb_breadahead_unmovable() and > > __breadahead_gfp() helpers which use non-movable memory for buffer > > head allocations and use them for the ext4 superblock readahead. > > > > v2: found a similar issue in __ext4_get_inode_loc() > > > > Fixes: 85c8f176a611 ("ext4: preload block group descriptors") > > Signed-off-by: Roman Gushchin <guro@...com> > > Reviewed-by: Andreas Dilger <adilger@...ger.ca> Hello, Theodore! Can you, please, pick this patch? We've some changes on the mm side (more actively using a cma area for movable allocations), which might bring a regression without this ext4 change. Thank you! Roman
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