Date: Fri, 7 Jun 2019 17:56:56 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: Slawa Olhovchenkov <slw@zxy.spb.ru> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r348772 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs Message-ID: <1e0ac4cf-d737-fbfd-a9b7-f728ef654d0a@FreeBSD.org> In-Reply-To: <20190607130429.GH47119@zxy.spb.ru> References: <201906070635.x576ZgEE027350@repo.freebsd.org> <20190607130429.GH47119@zxy.spb.ru>
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On 07/06/2019 16:04, Slawa Olhovchenkov wrote: > On Fri, Jun 07, 2019 at 06:35:42AM +0000, Andriy Gapon wrote: > >> Author: avg >> Date: Fri Jun 7 06:35:42 2019 >> New Revision: 348772 >> URL: https://svnweb.freebsd.org/changeset/base/348772 >> >> Log: >> Restore ARC MFU/MRU pressure >> >> Before r305323 (MFV r302991: 6950 ARC should cache compressed data) >> arc_read() code did this for access to a ghost buffer: >> arc_adapt() (from arc_get_data_buf()) >> arc_access(hdr, hash_lock) >> I.e., we first checked access to the MFU ghost/MRU ghost buffer and >> adapt MFU/MRU sizes (in arc_adapt()) and next move buffer from the ghost >> state to regular. >> >> After r305323 the sequence is different: >> arc_access(hdr, hash_lock); >> arc_hdr_alloc_pabd(hdr); >> I.e., we first move the buffer from the ghost state in arc_access() and >> then we check access to buffer in ghost state (in arc_hdr_alloc_pabd() >> -> arc_get_data_abd() -> arc_get_data_impl() -> arc_adapt()). This is >> incorrect: arc_adapt() never see access to the ghost buffer because >> arc_access() already migrated the buffer from the ghost state to >> regular. >> >> So, the fix is to restore a call to arc_adapt() before arc_access() and >> to suppress the call to arc_adapt() after arc_access(). >> >> Submitted by: Slawa Olhovchenkov <slw@zxy.spb.ru> >> MFC after: 2 weeks >> Sponsored by: Integros [integros.com] >> Differential Revision: https://reviews.freebsd.org/D19094 > > Include in 11.3-RELEASE planed? I didn't plan it, given the release schedule. But I can be convinced that this is a really important fix. So far, I am not :) -- Andriy Gapon
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